Chapter 8 _ Điều hoà ở mức độ RNA _ bài dịch phan văn nam

8/14/2019 Chapter 8 _ iu ho mc RNA _ bi dch phan vn nam

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Chng 11:

IU HA DCH M CP RNA

iu ha cp RNALin kt ca Protein ti ARN iu khin t l suy thoiMt s phn t mRNA phi c tch ra trc khi dch mMt s phn t protein iu khin c th l nguyn nhn c ch dch

mMt s phn t protein iu khin c th kch hot dch mQu trnh dch m c th c RNA i ngha iu khin

iu khin qu trnh dch m bng s bin i RibosomeRNA can thip ( RNAi)S nhn bi v lan truyn ca RNAiPTGS (bt hot gen trong sau phin m) trong thc vt v s ch ng

trong nmMicro RNA mt lp ca RNA iu khin nhS suy gim l nguyn nhn gy kt thc qu trnh phin m sm

RNA

Riboswitches - RNA tc ng trc tip nh mt c ch iu khin

iu ha cp RNA1


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iu ha cp RNA

iu ha s biu hin ca gen mc phin m l hiu qu nhtrong bo tn nguyn vt liu v nng lng trong khi iu ha hot nca enzyme cho hu ht cc phn ng din ra mt cch nhanh chng. Vrng iu ha cp dch m khng phi l hiu qu nht v cng kh phi nhanh chng nht, bi th n thng xuyn xy ra t hn cc hnthc iu ha khc. Thng thng, mt khi mRNA c to ra, nnhanh chng chuyn n ribosome ni n c dch m. iu ny c bing trong sinh vt prokaryotic l sinh vt khng c mng nhn hn chs n gn ca b my phin m v cc ribosomes. tng c kin chrng s iu ha dch m n l rt him. Phn no iu ny l do nhnkh khn ln hn ca phm vi dch m v lin quan n hin tng nhmRNA n nh hn l cp th nghim phin m hay protein. Do gn y cng vic tit l mt s lng ngy cng ln cc trng hiu ha mc dch m, c bit l trong cc sinh vt nhn tht. Tron, thc vt dng nh u tin iu ha dch m thng qua vic s dnmt s t cc phn t RNA nh iu khin. Tuy nhin, vn cn c nhnngi bit t hn cc trng hp iu ha dch m so vi iu ha phim.

Ngoi vic kim sot qu trnh dch m ca mRNA ngay sau khi ntng hp, vn cn c kh nng xy ra s ngn chn qu trnh tng hp cRNA thng tin sau khi qu trnh phin m c bt u v ch mt onngn RNA c tng hp. Mt t c ch cn cha r rng ny c quvo nh l c ch suy gim qu trnh phin m. i khi n c phn lonh l mt dng ca iu ha qu trnh phin m. Tuy nhin, n c bao gm trong chng ny, v n lin quan cht ch n iu ha dch mm cc thay i cu trc RNA thng tin c lin quan trong c hai trnghp.

iu ha cp RNA2


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Nhiu trng hp iu ha qu trnh dch m bit xy ra nh l c bc ngoi trong bc phc h iu ha mc cao cng bao gm iha mc phin m v hot ng ca protein. Cc v d bao gm cc phn ng sc nhit c vi khun v nhiu ng vt v kim sot tc tng trng ca t bo v khc bit trong cc ng vt bc cao. Trongchng ny, chng ti c gng minh ho s iu ha cp RN bng cch s dng cc v d a ra cc c ch iu ha khng qu phtp.

Trc khi tng hp mt phn t mRNA, c mt s con ng mtrong s dch m ca thng tin c th c iu khin:

1. Kim sot i vi t l suy thoi ca mRNA2. S bin i RNA khng dch m thnh dng c th c dch m3. Cc protein iu khin kim sot s dch m ca mRNA4. S lin kt ca RNA i ngha vo mRNA ngn cn qu trnh

dch m5. Kim sot s dch m ca mRNA bi riboswitches.6. u tin dch m ca mt s lp mRNA no do s bin i ca

ribosome.

Lin kt ca protein vo mRNA iu khin t l ca s suy thoi

Khng ging nh cc DNA cu to nn gennom t bo, thi gian tnti ca mRNA l tng i ngn. Tt c cc t bo u cha mt lot ribonucleases c vai tr loi b mRNA mt khi n phc v chc nngThi gian bn hy ca mt mRNA in hnh trong vi khun nh E. coli l2-3 pht. Tnh mn cm vi s suy thoi ca mRNA ph thuc vo ctrc th cp v v vy mt s phn t mRNA c n nh hn nhn phn t khc. y chng ti ang quan tm n trng hp mn cm vs suy thoi ca mRNA c thay i phn ng li tn hiu iu hS suy thoi mRNA c th c cn tr hoc thc y do s lin kt cRNA c trng vi cc protein iu khin. S gii thch chnh xc v cch thng kh khn v s lin kt vi ribosomes bo v mRNA trns suy thoi. V vy m mRNA khng c dch m s b suy thoi nhanh

iu ha cp RNA3


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hn. C hai con ng chnh trong lin kt ca mt protein c th nhng n s n nh mRNA. Th nht, n c th thay i trc tip smn cm ribonuclease tn cng. Th hai, cc protein c th gip hoc cn tr lin kt vo ribosome, m c th thay i tc dch m, vgin tip nh hng n s n nh mRNA.

H thng iu khin CsrAB ca E. coli bao gm mt RNA lin kvi protein, CsrA, v mt phn t RNA m ha, CsrB, hot ng nh lmt ni u cho CsrA. Protein CsrA c th lin kt vi mi phn tmRNA m n iu ha hoc ti RNA CsrB. Mi RNA CsrB c thcha khong 18 protein CsrA. Cc h thng iu khin CsrAB kim socn bng gia cc ng d tr nh glycogen, c tch ly trong vkhun, c bit l trong pha tnh, v s phn chia ca ng bngglycolysis (CSR = carbohydrate storage regulator). Ni chung, CsrA kchhot glycolysis v ngn chn tng hp glucose v tng hp glycogen.

Cc h thng CsrAB kch hot cc operon flhDC bng s n nhca mRNA. Nhng s kin chnh c th tho lun. Lin kt ca CsrA vmRNA c th trc tip kch hot dch m. Ngoi ra bo v cc mRNA ts suy thoi bi ribonucleases s gin tip tng qu trnh dch m. ProteinCsrA cng lin kt vo mRNA mang cc gene tham gia vo vic tng hpglycogen (Hnh. 11.01). S lin kt ca CsrA y nhanh s phn hy camRNA g/g ca n ngn cn s dch m. Mt ln na, c hai cch tron c nhng lin kt ca CsrA c th nh hng n s n nh mRNA N c th thc y enzyme ribonuclease tn cng trc tip hoc c thngn cn qu trnh dch m u tin, trong c trng hp mRNA skhng c bo v bi cc ribosome v s b thoi ha nhanh hn. Quynh th nghim gia mt trong hai cch khng phi l d dng.

Mt S Phn T mRNA Phi c Tch Ra Trc Khi Dch M

Eukaryotic cc phn t mRNA l kt qu ca s x l v loi bcc intron v gn thm ui v m so visn phm phin m u tin(primary transcript) (xem Ch.12 bit thm chi tit). Ni chung,mRNA prokaryotic khng c x l theo cch ny. Sn phm phin m

iu ha cp RNA4


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u tin c thc hin bi enzyme RNA polymerase, thng l RNAthng tin trong prokaryotes. Tuy nhin, trong mt vi trng hp him hoi,mRNA prokaryotic tip tc x l l cn thit trc khi n c th dcm.

Hnh 11/1: Kim sot s suy thoi ca mRNA bng CsrAn nh ca mRNA glg c iu ha bng protein CsrA. Trong khi

khng dng n, cc RNA lin kt vi protein CsrA lin kt vi RNA CsrB Khi protein CsrA lin kt vi mRNA glg, cu hnh ca mRNA glg, hndng ca mRNA glg thay i tr thnh dng d b phn hy

Trong Escherichia coli,ribonuclease III l mt trong mt sribonucleases ch yu tham gia vo vic x l trc cc tRNA v rRNA Ngoi ra, mt s phn t mRNA phi c x l bng RNase III trc kh

iu ha cp RNA5


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chng c th c dch m. Cc mRNA t gene speF m hadecarboxylaza ornithin dch m tt hn gp bn ln nu ct bng RNasIII. Tuy nhin, mRNA t geneadhE , m ha enzyme dehydrogenazaalcohol, yu cu x l bng RNase III l tuyt i. Trong nhng trnghp nh vy, phn t mRNA ban u gp li n mc v tr lin kt cribosome v m m u khng ti gn c. Tch mRNA ngc ln trnca v tr lin kt ca bng RNase III lm cc trnh t ny c gii phn cc ribosome nhn ra (Hnh 11/02). Trong nhng th t binrnc, mthiu RNase III, cc mRNA adhE khng th c dch m v cc t bokhng th pht trin ln mnh trong ln men k kh.

Hnh 11/02: S tch ra ca mRNA adhE bng RNase IIIV tr lin kt ribosome ca mRNA adhE c th khng c lin k

vo ribosome do tin mRNA gp li. RNAase III tch cc tin mRNAadhE v vy bc l v tr lin kt ribosome.

iu ha cp RNA6


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Ph hy thng tinadhE cng c kim sot bng s hot ng caribonuclease. mRNAadhE trng thnh lm thoi ha bng ribonucleaseG, ribonuclease bnh thng khc tham gia vo qu trnh x l rRNA.Trong th t binrng , thiu RNase G, chu k bn hy ca mRNAadhE s tng ln t 4 n 10 pht, mc tng ln v protein adhE c snxut qu mc.

RNA v ngha (non-coding RNA): mt vi phn t RNA no khng c dch m to protein

Sn phm phin m u tin (primary transcript): phn t RNA u tin thu c t mt mch khun DNA phin m, trc khi x l hoc si xy ra

ribonuclease III : mt ribonuclease ca vi khun c chc nng chnhl x l nhng rRNA v tRNA tin thn

Mt S Protein iu Khin C Th L Nguyn Nhn Km Hm QuTrnh Dch M

Cng nh mt s protein iu khin c th lin kt vo DNA v thcy hoc ngn cn qu trnh dch m, mt s protein cng c th lin kvo nhng trnh t c bit trn mRNA v iu khin qu trnh dch mCc v d v c hai qu trnh iu ha dch m tch cc v tiu cc bit n. Nhng phn ng ca mRNA vi st c thng dng di nh l mt v d v s km hm qu trnh dch m.

St l mt dinh dng cn thit v l nhn t ng tc ng (cofactorcho nhiu protein, chng hn nh cytochromes v hemoglobin. Tuy nhin,st t do to ra cc gc t do v c hi do nguy him. Do vy, nguyt st d tha c tch tr vo ferritin cn prokaryotic l bacterioferritin. Ferritin l mt protein hnh cu lm bao gm 24 tiu nv. Tnh n 5000 nguyn t st c th c lu tr nh phc hhydroxyphosphate bn trong hnh cu ny.

Mc ferritin c iu tit p ng li ngun d tr st. Trothc vt, mc ferritin c iu ha mc phin m. Tuy nhin

iu ha cp RNA7


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trong c ng vt v vi khun, mc ferritin ph thuc vo s iu hqu trnh dch m. Khi thiu st, qu trnh dch m ca mRNA ferritin ct gim. Khi st phong ph ferritin c tng hp nhiu. Trong ng vmt RNA lin kt vi protein chu trch nhim, trong khi vi khun kim sot bng RNA i ngha (antisense RNA) (xem di y).

Bacterioferritin : Cc vi khun tng t ca ferritin, mt protein cdung lng st

Ferritin : mt protein tch ly st translational repression(s km hm qu trnh dch m):hnh thc

kim sot trong s dch m ca mt RNA thng tin b ngn cnVng 5 khng dch m (5-UTR) ca ferritin mRNA ng vt cha

mt trnh t c bit c bit n nh l mt yu t p ng st (iron-responsive element (IRE)), mt dng c cu trc khung loop. Khi stkhan him, mt phn t protein iu khin st (iron regulatory protein(IRP)) lin kt vo thn v loop IRE v ngn cn dch m. Kt qu cavic b sung thm st dn n s tch ra ca IRP t ferritin mRNA, do n c th c dch m (Hnh 11/03).

Vng 5 khng dch m (5 -untranslated region( 5-UTR ): Trnh t khng c dch m nm gia u tn cng 5 v m m u ca mmRNA

Protein iu khin st (IRP): Nhn t iu khin s dch m kim sot s biu hin ca mRNA ng vt phn ng li mc st

Yu t p ng st (IRE):v tr trn mRNA IRP lin kt

iu ha cp RNA8


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Hnh 11/03: iu ha s dch m ca Ferritin mRNA bng IRPCc mRNA ferritin c mt cu trc quai (loop) (cc yu t p ng

st hoc IRE) trong vng 5 khng dch m. Khi st khan him, cc proteiniu khin st (IRP) lin kt vi tiu phn nh ca ribosome t lin kt vcu trc m ca cc mRNA ngn cn s khi u dch m. Khi s phong ph khng c IRP n lin kt v s dch m xy ra.

Hnh 11/04: Hot ng Aconitase chng li s lin kt ca RNAvi IRP1

iu ha cp RNA9


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Cc protein IRP1 c tc ng nh mt enzyme (aconitase) khi st phong ph. Sau khi mt i mt nguyn t st t trung tm nhm Fe4S4,trong hon cnh st khan him, hai vng chnh m, cho php lin kt vi RNA. Hu qu ca vic IRP1 lin kt vo mRNA l ngn cn qu trntng hp transferrin.

Trong ng vt, enzyme acid -aminolevulinic synthase xc tctng bc gii hn t l trong con ng tng hp cc cht st c cha nhn t heme. Khng ng ngc nhin, cc mRNA cha mt yu t png st v cng iu khin dch m di IRP. Cc th th cho protein vchuyn st transferrin, c tm thy trong mu, cng c iu khin bIRP lin kt vi mt IRE trn mRNA, nhng trong trng hp ny s nnh mRNA b nh hng.

S tp trung ca st t do trong cytoplasm c gim st trc tip bng protein iu khin st. Mc d c mt s IRP, mt IRP chnh, IRPging vi vi cc enzyme cytoplasmic,aconitase. Enzyme ny c mtnhm Fe4S4 cn thit cho enzyme hot ng. Khi st khan him, mttrong bn nguyn t st b mt t nhm Fe4S4. Sau aconitase/IRP1 menzyme hot ng v thay hnh dng, bc l v tr lin kt vi RNA. Vvy, khi st phong ph, aconitase/IRP1 hot ng nh aconitase (mtenzyme trong chu trnh Krebs chuyn i isocitrate thnh citrate) vkhi st him, n hot ng nh mt RNA lin kt vi cht km hm qutrnh dch m (Hnh 11/04).

iu ho bng cht km hm qu trnh dch m cng c s dng kim sot tng hp protein ribosome trong vi khun chng hn nh vkhun E. coli. Cc protein ribosome c trong mt vi nhm operon. ivi mi operon, mt trong nhng protein ribosome m ho lin kt vimRNA v t iu ha tng hp tt c cc protein trong operon. Nhn protein ribosome ny c u tin lin kt vo rRNA v ch c lin kvo mRNA ca ring mnh khi khng c mt ca rRNA. C ch ny m bo rng tng s ca rRNA v ribosomal protein c cn bng. Nu cmt protein ribosome vt qu rRNA khi qu trnh dch m s cgim xung (Hnh 11/05).

iu ha cp RNA10


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Hnh 11/05: iu Ha Qu Trnh Tng Hp Protein Ribosome Trong Vi Khun

Cc mRNA c hin th pha trn cng ca hnh c cha mt loop,mt v tr lin kt ribosome (RBS) v gene cu trc m ha cho mt s protetin ribosome. Nhng protein ny u tin lin kt vo rRNA. Trong

nhng trng hp khng c rRNA lin kt vi cc protein ribosomemt trong s chng lin kt ring vi mRNA ca mnh v bin i cc chnh chn cc v tr lin kt vi ribosome. iu ny ngn cn qu trnhtng hp qu gii hn ca protein ribosome.

iu ha cp RNA11


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Aconitase:Mt enzyme ca chu k Krebs, trong ng vt, cng hot ng nh mt protein iu khin st

Nhm Fe4S4 : mt nhm gm nguyn t v c st v lu hunhc tm thy nh l mt cofactor trong vi protein

Cht km hm dch m (translational repressor): Mt protein lin kt vi mRNA v ngn cn s dch m

Mt S Protein iu Khin C Th Hot Ha Qu Trnh Dch M

iu khin dch m tch cc c s dng kim sot s tng h protein trong lc lp sau khi c nh sng kch thch. Tng hp ca nhi protein lc lp cng nhiu cng tt gp hng trm ln bi nh sng. Cmc ca mt s protein ny c kim sot bng s phin m, mt skhc bng dch m v mt s khc na bng s thoi bin protein.

V d, mRNA cho tiu n v ln ca Rubisco tch ly trong qu trnh pht trin lp th ngay c trong bng ti. [Rubisco l ribulose bisphosphatcarboxylase, mt enzyme quan trng trong s c nh ca mt lng khcarbon dioxide trong qu trnh quang hp. l protein phong ph nhttrn tri t.] Mt v d khc l PsbA (= D1 protein) l thnh phn ca hthng quang hp II. S dch m ca cc mRNAs ny c kim sot bngnhng protein m ha ca nhn c hot ng nh cht hot ha qu trnhdch m. Nhng protein ny lin kt vo vo mt vng giu adenine trongvng 5-UTR ca mRNA. Cc cht hot ha lin kt vo mRNA di nhsng v cho php dch m. Trong bng ti, chng khng lin kt vomRNA khng c dch m do cu trc cu trc th cp bt li ca n(Hnh 11/06).

Cc cht hot ha qu trnh dch mcPABP (chloroplastpolyadenylate binding protein) tn ti hai hnh dng, ch mt trongtrong s c th lin kt vi RNA. S chuyn i trong hai dng cPABc kim sot bng nh sng. Cc in t c kch thch t h thnquang hp I c i qua mt chui vn chuyn in t ngn ti cPABP Nhng in t ny bin i dng disulfide ca cPABP thnh dn

iu ha cp RNA12


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sulfhydryl. Vic kh dng sulfhydryl c th lin kt vo RNA v kch hodch m, trong khi, dng disulfide khng th dch m (Hnh 11/07).

cPABP (chloroplast polyadenylate binding protein ) mt protein hot ha qu trnh dch m iu khin s biu hin mRNA ca lp th.

Rubisco (ribulose bisphosphate carboxylase ) Mt enzyme quan trng trong vic c nh kh carbon dioxide trong qu trnh quang hp

translational activator ( cht hot ha qu trnh dch m) Mt protein lin kt vi mRNA v xc tin s dch m

Hnh 11/06: S hot ha qu trnh dch m mRNA lc lp

Trong bng ti, loop trung tm trong mRNA ngn cn cc mRNA lin kt

iu ha cp RNA13


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vo ribosome. Khi c y nh sng, mt mRNA lin kt vi protein lm RNA dui thng ra ribosome lin kt.

Qu Trnh Dch M C Th c iu Khin Bng RNA i Ngha(RNA antinsense )

Ch c mt mch DNA c dng lm khun sao m thnh phn tRNA thng tin. iu ny c lin quan n tng mch khun ring, mchkhng m ha hay mch i ngha. Do , cc mRNA c sn xut lRNA c ngha. Mch khc ca DNA (mch m ha hay mch c ngha)thng khng c s dng nh l khun cho qu trnh dch m. NuRNA phin m s dng mch m ha lm khun nh chng ti s sn xumt phn t RNA b sung trong trnh t mRNA. iu ny c gi lRNA i ngha v c th c baz kt cp b sung vi mRNA ca n, cnging nh hai mch ca DNA trong gene gc c cc baz kt cp vnhau (Hnh 11/08). [Lu rng uracil kt cp vi adenine trong hai RNA]

iu ha cp RNA14


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Hnh 11.07: Hnh dng ca cht kch hot dch m cPABP phn ng li cng nh sng

Mt chui phn ng nh sng trong h quang hp II (PS II) v I(PS I)ca lc lp thc vt nh mt in t chuyn i thng qua chuvn chuyn in t. Cc in t kh cu ni disulfide ca cPABP v vhnh dng ca n thay i v cho php n lin kt vi mRNA v kch ho s dch m.

iu ha cp RNA15


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Hnh 11/08 : RNA i ngha c th c baz kt cp vi mRNA mRNA thng c to ra t mch mt mch khun l mch khn

m ha ca DNA. Nh vy mRNA c bit nh l RNA c ngha. N RNA c to ra t mch khun l mch m ha, n s b sung trongtrnh t mRNA v n c bit nh l RNA i ngha. Mch RNA c nghv i ngha c th kt cp baz.

antisense RNA ( RNA i ngha):Mt phn t RNA b sung cho mRNA

sense RNA (RNA c ngha): RNA bnh thng c sn xut t mch khng m ha ca DNA

RNA antisense (RNA i ngha) i khi c s dng trong iu hagen trong c vi khun v sinh vt nhn chun. Nu antisense RNA to ra, cc baz ca n s kt cp vi mRNA v ngn cn n lin kt vribosome v dch m c thc hin. (Hnh 11/09). Trong thc t, RNAantisense khng c to ra bng si khng phi l khun ca cng mgene to ra mRNA phin m. Kh khc bit "khng gene" c dng to ra RNA antisense.

Bacterioferritin l protein ca vi khun c s dng d tr bsung thm cc nguyn t st. Cc genebfr m ha bacterioferritin bn thnv gene khngbfr m ha cc RNA i ngha.

iu ha cp RNA16


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V ch mt on ngn ca RNA i ngha l cn thit chn mRNAcc gene khng tng t nh trong trnh t nhng ngn hn gene nguyn bn. Khi nui cy lng st tp trung thp, khng cn bacterioferritinnhng n to ra nu mc st tng ln. Gene bfr phin m ca n phin m to ra mRNA trong c hai iu kin. Tuy nhin, gene khng bfr c kim sot bng mt protein iu khin c gi l Fur (FerriUptake Regulator(yu t iu khin s hp thu st III)), c kh nng nh bit c cc cp ca st.

Khi lng st c mt phong ph, Fur hot ng nh l mt cht kmhm v lm tt qu trnh phin m ca hng t hoc hn na cc operoncn thit thch ng cho cc t bo khan him st. Bao gm cc gene mt sh thng hp thu st c thit k nm bt theo di mc dinh dcn thit ny. Ngoi ra, Fur tt gene khng bfr, m bt gen sn xut c bacterioferritin (Hnh 11/09). Trong lng st thp gene khng bfr c phin m to ra RNA i ngha. iu ny ngn cn tng hp proteica bacterioferritin khi st l khan him. Do , bng cch s dng RNAi ngha, mt trong nhng gene c th c iu ha i din vi mnhm khc mc d tt c u phn ng li vi cng mt tc nhn kcthch.

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Hnh 11/09: RNA i ngha iu khin tng hp Bacterioferritin Cc chromosome vi khun c cha gene cho c mRNA bfr v RNA khngbfr. Nu c hai phn t RNA c phin m, RNA khng bfr kt cp vmRNA bfr v ngn cn n dch m. Khi st phong ph, gene khng bfr khng c biu hin v ch mRNA bfr c sn xut. Di cc iu kidch m ca mRNA bfr cho bacterioferritin c th din ra

Tng hp RNA i ngha nhn to s can thip vi s biu ca genhay bt k qu trnh t bo no lin quan n RNA. V d, RNA i nghaang c kim tra qua th nghim ngn chn bnh ung th bng dnli qu trnh phn chia nhim sc th.

iu Ha Qu Trnh Dch M Bng Nhng S Bin i Ribosome

Cng ging nh cc ribosome phi dch m t nhiu thng tin khcnhau, c din t di rt nhiu nhng iu kin khc nhau. Khng ngnhin, cc ribosomes ca chng him khi c sa i, ngoi tr trnhp chung l ton b ribosomes vo d phng gim tng t l tng hton b protein trong cc t bo khng pht trin, nh c tho lun tronChng 8.

Mt trong nhng trng hp ngoi l him hoi l s phosphoryl haca protein S6 ca tiu phn nh ca ribosome trong t bo ca loi nvt c v. Cc protein S6 c th c phosphoryl ha n nm ln trnmt cm ca cht tha serine gn vi phn cui C ca n. [ sinh vt nhchun bc thp, chng hn nh nm mem thiu nhng v tr phosphoryha ny.] S phosphoryl ha xy ra sau khi cc t bo trong mt m ang pht trin nhn c mt tn hiu tng nhanh. Vic u tin ribosomesa i dch m nhng phn t mRNA c 5-Terminal oligopyrimidine(5-TOP)

5/-Terminal oligopyrimidine tract (5-TOP): Nhng b giu pyrimidine ko di nm gia u tn cng 5 v m m u ca mRNA.

Fur (ferric uptake regulator)( iu khin s hp thu st III) : proteiniu khin chung vi nhiu mc st trong vi khun

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Vic sa i ribosomes u tin dch m cc phn t mRNA c 5-Terminal oligopyrimidine (on kt thc gm on ngn pyrimidine) (5-TOP) (Hnh 11/10). y l nhng trnh t giu pyrimidine c v tr ti utn cng 5 ca mRNA, ngc ln m m u.

N sn xut ra hu ht cc mRNAs u tin m ho protein ribosomev s ko di cc yu t. Ni cch khc, s phosphoryl ha protein S6 kchthch ribosome to ra nhiu hn ribosomes tin ha mi phn nli t l tng trng v phn chia t bo.

RNA Can Thip (RNAi) RNA can thip (RNAi)l mt c ch bt hot gene gy nn bi

RNA mch kp (dsRNA). l trnh t c bit v lin quan n s suythoi ca c hai loi phn t RNA: RNA si kp (dsRNA) v RNA si nthng mRNA l nhng si tng ng trong trnh t dsRNA lm kchhot phn ng tr li.

l kin cho rng ngun gc ca RNAi nh l mt c ch bo vchng li vi rt. Trong sut qu trnh din bin ca cc s kin, nhng t bo cha dsDNA v ssRNA nhng RNA si kp li khng tm thy. Tuynhin, trong khi nhim bnh bi hu ht RNA ca cc loi vi-rt, cgenome ca vi rt thng qua dng trung gian l si kp RNA (nhng bnsao trung gian). iu ny ng cho c hai loi virt rng chng mang theogenomes nh ssRNA trong cc tiu phn ca virus v nhng loi s dndsRNA (xem Ch. 17 virus). Do vy, dsRNA c xem l mt tn hiu chocc nhim trng v gy nn mt tr li chng li vi rt.

RNA can thip c kch hot bi dsRNA c y cc cp baz vc t nht 21-23 cp baz. Cn nhng phn t dsRNA di s c l cthnh nhng mnh c di khong 21-23 bp bi mt nuclease c gl "Dicer" (Hnh 11/11). Nhng mnh RNA c gi tt l siRNA (RNAngn can thip) v lin kt bi protein ca RNA-phc h gy nn s imlng (RISC). Nhng phc h RISC nhn ra v lm suy bin RNA si tng ng trong trnh t siRNA. iu ny bao gm vic tho ra v phn lyca si siRNA trong phc h RISC v xy ra sau cp baz vi RNA ch

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Vi sinh vt phn t

trong Hnh. 11/11. Hot ng ca cc nuclease trong phc h RISC, ikhi c gi l "Slicer", sau lm thoi ha RNA ch.

Hnh 11/10: S phosphoryl ha ca S6 to cho mRNA c 5-TOP Cc protein S6 ca tiu phn nh ribosome c th c phosphoryl

ha bng mt protein kinase kch hot. Nhng mRNA ny c mt di trnu 5 sau s lin kt tt hn vi ribosome v bt u dch m .

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Hnh 11/11: C ch ca RNA can thipRNA si kp xm nhp (dsRNA) c tha nhn(bi RDE-4 v

cc protein trong Caenorhabditis). Dicer tch cc dsRNA vo phn onca 21 hay 22 nucleotides vi mt hoc hai baz nh ra- RNA can thipngn (siRNA). iu ny c tha nhn bi RDE 1 l cc RNA-phc h gy bt hot do RNA (RISC). Nhng mch ca siRNA c tch trong qutrnh hot ha RISC. Cui cng, RISC tch RNA ch thnh nhng ontng ng vi cc siRNA.

RNA si kp thng c tiu hu bi cc t bo sng ca tt c c sinh vt.

RNA can thip tiu hy RNA thong tin c trnh t ging nh RNA skp c pht hin trong cc t bo.

Dicer : Ribonuclease tch RNA si kp thnh nhng phn on 21-23bp

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Vi sinh vt phn t

Phc hp lm bt hot do RNA gy ra (RISC): phc h protein gy nn bi siRNA phn hy RNA si n tng ng trong trnh t siRNA

RNA can thip: c ngha l p ng c kch hot bi s hin dinca RNA si kp v l kt qu trong suy thoi ca mRNA hoc nhng b sao RNA tng ng khc.

short interfering R N A (siRNA): nhng phn t RNA si kp gm 21-22 nucleotides tham gia vo vic kch hot RNA can thip trong sinhvt nhn chun.

Slicer: Ribonuclease hot ng ca phc h RISC RNA can thip ca sinh vt nhn chun hot ng trong mt phm v

rng khp, bao gm c ng vt nguyn sinh, ng vt khng xng snng vt c v v thc vt. N khng c tm thy trong sinh vt nhs. [Trong vi khun, ribonuclease III nhanh chng lm thoi ha phn tdsRNA ngn nh 12 bp.] Nhng nghin cu gn y cho thy s phc tca tng n gin, s thoi ho RNA ch duy nht thng qua cc hong RNAi. RNAi c lin quan n cc c ch c th im lng s phin mca gen ch do bin i cu trc chromatin v thc y s methyl haDNA.

S nhn bi v lan truyn ca RNAi

RNAi c hiu lc c bit. V vy, ch di 50 phn t ca siRNA cth lm bt hot RNA ch c mt trong hng ngn bn sao ca mi t by l cc kt qu t s nhn bi ca siRNA qua mt RNA polymerase ph thuc RNA (RdRP) m khng cn phi c on mi (Hnh 11/12). Ccc mRNA ch bi Slicer gy ra hai phn t RNA khc thng v khngn nh, mt phn t c gn m nhng thiu ui poly (A) v phn tkhc c ui nhng khng c gn m. Mt hoc c hai phn t RNA bthng hnh nh c s dng nh lm khun RdRP to ra dsRNASau dsRNA thc hin vai tr nh l cht nn cho Dicer, to ra nhiusiRNA nhn bi tc dng cc RNA can thip.

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Vi sinh vt phn t

RNA can thip c th c nhn bi v c th lan truyn khp mt cth, sau khi c kch hot trong mt vng khu tr.

RNA polymerase ph thuc RNA (RdRP): RNA polymerase s dn RNA nh l mt khun v tham gia vo s nhn bi ca RNAi phn ng

Hnh 11/12: S nhn bi ca RNA can thip bng RdRP RNA d thng c to ra bi RISC - gin tip phn tch c s

dng nh mt khun ca RNA polymerase ph thuc RNA (RdRP). iny to ra nhiu hn dsRNA ri c quay li chuyn thnh nhiu h siRNA bi Dicer

Ngoi s nhn bi, nh hng ca RNAi c kh nng lan rng t ct bo n t bo, v c th di chuyn trong khong cch ln xuyn sumt c th. Hiu ng c bit ny c th thy r trong nhng loi thc v

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Vi sinh vt phn t

(xem di y). S lan truyn ca tn hiu siRNA trn ton c th cngc thy trong ng vt. ng ch l, trong C. elegans cc RNAi chiu lc trn l thng qua vi th h (khng c sa i trong trnh tgenomic DNA ca gene ch tm thy). Loi ng vt c v khng cnhng RdRP chu trch nhim v s nhn bi RNAi, v vy vn cn nhn ph tch vng khu tr RNAi. l suy ngh rng s pht trin ca h midch c trng ca tng loi lm RNAi t quan trng trong nhng loing vt c v.

p dng Th nghim ca SiRNA

RNAi ang c s dng rng ri trong phng th nghim nghin cu ngn chn s biu hin ca gene (nh i lp vi thng tin di truyn cvi rt). RNAi trong cc ng vt ln u tin c tm thy vi su hntrn Caenorhabditis elegans. Khi tim dsRNA vo C. elegans l nguynnhn phn hy cc mRNA ca trnh t tng ng v qua dng s biuhin ca gene ti cp sau phin m. RNAi hin ang c s dng nghin cu chc nng ca gene trong C. elegans, t khi trnh t genomehon thnh c hiu lc bi vy c th l tng hp siRNA tng ng v bt c gen no cn quan tm.

Vic s dng RNAi cho php nghin cu v chc nng gene mkhng cn phi thc hin nhng t bin vi s thay i hoc phin bkhng hot ng ca mt gene ring bit. iu ny c bit hu ch chnhng sinh vt nhn chun, hu ht u th lng bi v ni phn tchtruyn kinh in do i hi phi a t bin vo c hai bn sao.

RNA can thip hin ang c c s dng rng ri nghin cchc nng gene trong nhiu ng vt v thc vt.

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Hnh 11/13: Gii Thiu Th Nghim Ca RNA Can Thip RNA can thip xy ra khi c hai RNA c ngha v i ngha ca m gene c mt v dng dsRNA. Hai sn phm thit k c hin th trtip cho s tng hp ca mt phn t dsRNA. Sn phm thit k th nh(A) c mt vng c ngha v mt vng i ngha l cp baz. Mt phn

m ring r vng c ngha v vng i ngha v mt dng cu trc loopkp tc. Mt cp Promoter (B) c mt Promoter dch m trc tip chomch c ngha, v Promoter khc cho mch i ngha. Kt qu l to hai phn t RNA b sung nhau v to dng phn t dsRNA.

Tuy nhin, RNAi ca n rt nguyn thy, ngn chn nhng biu hinca tt c cc bn sao ca gene ch. Thc vy, RNAi c th c s dtrong nhng sinh vt ni cc bn sao ca gene c mt. V d, ng vnguyn sinh nh Parameciumcha hai loi nuclei, mt germline nhn sinh

sn v mt nhn to hn nh thuc th a bi (xem Ch. 19). Tnh trng ngy cho chng kh c tiu chun phn tch di truyn.Qua thc nghim, RNAi c th c gy nn bng cch cung cp

nhng phn t di ca dsRNA c ct thnh cc siRNA bi enzymeDicer (Hnh 11/11). Si n RNA i ngha chng li gene thuc t bocng c th kch hot RNAi bi cp baz tng ng thm vo si RNA

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iu ny to ra dsRNA bn trong cc t bo. Ngoi ra nhng phn tdsRNA ngn c chiu di khong 21.-23 nucleotides c th c qun ltrc tip v s hot ng nh siRNA.

Mc d dsRNA c th c cn c nh vy, thng thng s rt lthun tin hn cung cp xy dng mt DNA to ra dsRNAin vivo. iuny c th c thc hin bi ba bin d chnh (Hnh 11/13):

i. Mt on DNA n c phin m t mt Promoter n tora mt cu trc thn quai. Ti y cc mch c thm vo v bt i lintip nhng b phn ly bi mt on ngn cng ca DNA cn li nhnon khng c cp i v dng quai.

ii. Mt on DNA ca hai promoter i din. Do t cng mton dsDNA, mt promoter phin m t mch dng v promoter khc phin m t mch m.

iii. Hai phn on DNA, hai on ny ngc nhau v c hai u c promoter ring bit. Do mt trong nhng promoter phin m mchdng t mch c ngha ca DNA v mt promoter khc phin m tmch m, ngc chiu, i ngha ca phn on DNA.

Cc dsRNA c to ra t cc DNA c th di (da vo Dicer tosiRNA) hoc ngn, trc tip cho siRNA.

Trong trng hp caCaenorhabditis elegans, dsRNA c th ctim vo trong su. Hoc su c th c lm thc n cho vi khun, chnhn nh E. coli, mang nhng plasmid vi DNA, nh c din t trn lto ra dsRNA in vivo. [Kh tin li, dng vi khun l ch n ung tnhin ca C. elegans.]

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Micro RNA (miRNA) c to ra bng qu trnh mt phn t tinthn gp li to cu trc thn quai. Dicer, ging nh nuclease to ra siRNA, phn ng li qu trnh ny. Sau phn ly hai mch., mt mchca miRNA lin kt vi mRNA ch v ngn cn qu trnh dch m.

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PTGS trong thc vt v s ch ng nm

Mc d c pht hin c lp, n ging nh lbt hot gen sauqu trnh phin m (PTGS) trong cy trng, ch ng trong Neurosporav RNAi trong ng vt gp mt c ch bo tn. H thng ny cng tm thy trong ng vt nguyn sinh nh Paramecium v nhm trng mikhoan. Trong c PTGS v RNAi s hin din ca dsRNA kch hot hthng Dicer/RISC to ra s thoi ha RNA. PTSG trong thc vt c thc truyn i nguyn vn trong ton b sinh vt t mt vng khi uiu ny c minh ha trong th nghim cy ghp, trong s bhot c truyn t m ghp vo thn chnh nhn c phn ghp. Cc thiu siRNA khuch i bi RdRP (xem trn) v sau truyn t t bn t bo qua plasmodesmata cho n khi chng n vi c h thnmch, phn phi cc siRNA trong ton b thc vt.

PTGS c quan st thc s trong thc vt mt vi nm trc khRNAi c pht hin ng vt. PTGS c nhn thy khi b sung c bn sao cc gene ca thc vt c a vo cc t bo thc vt l bk k thut di truyn. Thay v tng mc biu hin ca gene, nh chi, i khi l mt kt qu gim ln mc biu hin ca gene. iu nc minh chng do phn hy ca mRNA tng ng vi cc trnh t vo v xy ra bi mt c ch cht ch lin quan n RNAi, nh c mt trn cho cc ng vt. Quelling l mt hin tng tng t thy tronnm nh Neurospora. t bin cy Arabidopsis c khim khuyt trongPTGS biu hin tng s nhy cm ca mt s thc vt b nhim bnh RNvirus. iu ny mt ln na cho thy rng vai tr t nhin caPTGS/RNAi trong vic bo v chng li s ly nhim ca vi rt.

Mt lot cc k thut, th thut c s dng to ra RNA si kbn trong cc c th thc nghim.

RNA can thip hot ng tt trong thc vt v phn ng c ph phi xung quanh thc vt y thng qua h thng mch.

Bt hot gen sau phin m (PTGS): kiu thc vt ca RNA can thi phn ng li RNA si kp l kt qu trong s thoi ha ca mRNhoc cc cc bn sao RNA tng ng khc gy ra dsRNA

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Hnh 11/15: Hai Dng Cu Trc Th Cp Lun Phin Ca Vng Dn u Ca mRNA

Nhng trnh t trong vng dn u ca RNA thng tin c k hiul 1, 2, 3 v 4 c th cp baz ghp i theo mt trong hai cch sau: A).Cu trc kt thc sm ca mRNA l do cc cp baz ghp i to haidng cu trc ghp cp b sung v cu trc loop trong mRNA. loop thhai, trnh t 3 kt hp vi 4, l nguyn nhn ca kt thc. B) S kt thc th c ngn cn nu mt protein lin kt vo mRNA ti v tr 1, ch php v tr 2 v 3 kt cp vi nhau. iu ny to ra nhng "pre-emptor" vngn cn s hnh thnh yu t kt thc.

Ging nh RNAi, PTGS i hi s hnh thnh cc dsRNA. Thc vy,

PTGS c th gy cm ng trong thc vt bng s iu hnh cc phn onh ca dsRNA lm sn, ng nh RNAi gy cm ng trong ng vtTuy nhin, c s khc bit chnh gia PTGS v RNAi l dsRNA c thtch ly trong cy sau qu trnh phin m ca mt gen chuyn. Cc c chny cha c hiu r hon ton. Trong mt s trng hp qu trnh phim ca c hai mch DNA c a vo bi promoter i lp c th dn s hnh thnh RNA kp. Trong cc trng hp khc, s ghp cp baz c th xy ra trong ni ti gia cc vng c b sung trong chui. Tu

nhin, PTGS cng c th gy cm ng bng nhng gen chuyn n l phin m cao. l kin cho rng mRNAs khc thng i khi c cthc hin v hot ng nh cc khun cho mt RNA-ph thuc RNA polymerase (RdRP). iu ny sau to ra cc dsRNA.

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Micro RNA Mt lp ca RNA iu khin nh

Phn t RNA rt nh (miRNA) l nhng phn t RNA ngn c mtvi tnh cht chung vi siRNA. Tuy nhin, nhng phn t miRNA quynh s biu hin ca gene bng ngn chn s dch m ca mRNA chkhng thc y s thoi ha ca mRNA. Chng ngn cn qu trnh dchm bng cch lin kt vo mRNA, thng lin kt vo vng 3 khng dchm, t ph bin trong cc vng m ha .

micro RNA (miRNA) phn t RNA iu khin nh ca t bo nhchun

Nhng phn t miRNA c sn xut t nhng RNA tin thn dhn vi khong 70 nucleotide c phin m t gen trong nhim sc th Nhng phn t RNA tin thn cun gp to thnh cu trc thn quai (Hn11/14). Vng thng si kp sau s c ct bi Dicer, vi cng mnuclease to ra siRNA. Nhng phn t miRNA c 1-3 baz khng ghpi gia v v th y l s khc vi siRNA, l loi c y cc cp bz ghp i . Thay v Rde1 nhn ra c siRNA, cc miRNA c lin k bi cc protein c lin quan, Alg1 v Alg2 (trong C. elegans). Cng chachc chn phc h RISC sau lin kt vo miRNA v cc mch ring rhay khng (nh siRNA). Mt cch khc l cc mch ring r t pht tmiRNA cc cp ba z thiu st. Trong bt k trng hp no, mt trongnhng si ca miRNA sau lin kt vo mRNA ch. Tuy nhin, s ghpcp ba z thng khng phi l hon ho (nh vi siRNA). Kt qu l, qutrnh dch m ca cc mRNA b ngn chn, nhng mRNA khng b thoiha. C ch chnh xc ca s c ch qu trnh dch m hin nay l khnr rng.

Micro RNA c tm thy giun, cn trng, loi ng vt c v v c thc vt l nh nhau gia cc sinh vt m RNA can thip biu lMiRNAs u tin c tm thy trong C. elegans, ni chng c gi lRNA thi gian nh (stRNA) v chng quy nh thi gian pht trin ca sutrong qu trnh chuyn dng ca cc con su non ti su trng thnh. Nhiu miRNAs xut hin c tham gia vo vic iu tit s pht triv c rt nhiu ch cho miRNA nh mRNAs l nhng yu t m ho cho

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qu trnh phin m, trong ln lt iu khin s biu hin ca cc gekhc.

Kt Thc Sm Nguyn Nhn Suy Gim S Phin M Ca RNA

S suy gim qu trnh phin m l mt c ch iu khin lin quann s kt thc sm qu trnh tng hp mRNA. Nhng nguyn l c bca s suy gim ln u tin mt phn ca mRNA s c thc hin, vdn u, c th gp ln to thnh hai cu trc th cp xen k. Mt tronnhng cu trc cho php tip tc s phin m nhng cu trc th cp khl nguyn nhn kt thc sm qu trnh phin m. Tnh trng ca s suygim cn cht khng r rng. N thng c xem nh l iu ha m phin m. Tuy nhin,n li c lin quan n vic mRNA c phinm mt phn. Do vy i khi n c xem nh l iu ha "sau qu trnh phin m". T khi s suy gim c lin quan cht ch vi cc c ch khxen k gia cu trc kt cp b sung v cu trc loop ca RNA, ti ch cho n cng vi cc hnh thc iu ha khc ca RNA.

Thng thng, vng dn u cha bn tiu vng (trnh t t 1 n 4c th kt cp baz theo hai cch khc nhau. Khi khng c cc yu t khcan thip, trnh t 1 kt cp vi trnh t 2 v trnh t 3 kt cp vi trnh t4, do to thnh hai cu trc kt cp b sung v cu trc loop (Hnh11/15). Cu trc th hai ca cu trc kt cp b sung v cu trc loopcha trnh t ghp cp 3 v 4, hot ng nh l mt nhn t kt thc. Tunhin, thay v trnh t 2 c th kt cp vi trnh t 3. iu ny xy rmt protein phi lin kt vo trnh t 1 v g b n khi phm vi hong. Cc kt qu tip ni l to loop kt thc, thng bao gm trnh tv 4, dng ny khng tn ti lu v qu trnh dch m ca mRNA c thtip tc.

iu ha bng s suy gim stem bao gm s lun phin gia cu trckt cp b sung cu trc loop trong mRNA.

S suy gim (attenuation):mt dng ca iu ha qu trnh phinm tc ng bng cch to s kt thc phin m sm v ph thuc vo s

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lun phin gia cu trc ghp cp b sung v cu trc loop trong vng dn u ca mRNA

Vng dn u( leader r egion ): vng pha trc ca mt phn t mRNA ca cc gen cu trc, c bit l khi tham gia vo s iu ha bngc ch suy gim.

S suy gim c s dng iu khin cc gene cho sinh tng hcc axit amin trong c hai loi vi khun gram m, chng hn nh E. coliv vi khun gram dng, v d nh Bacillus. Nu ngun d tr acid amidi do th cc gene sinh tng hp nn n phi c c tt. Ngc lnu mc ca cc acid amin thp, cc gene sinh tng hp nn n s phin m.

Trong E. coli, s suy gim c s phc tp v thng lin quan n slin kt ca cc ribosome vo vng dn u ca mRNA , ni m chngdch m ra mt peptide dn u. Peptide dn u c m ho bng mkhung c m ngn v ch bao gm 14 hoc 15 axit amin. N nm st vu tn cng 5 ca mRNA, ngc dng ca cc gen cu trc cho ccenzymes ca con ng sinh tng hp (Hnh 11.16A).

Peptide dn u cha mt s n v m lin tip cho cc acid aminnghin cu. V d, trong peptide dn u ca operonhisca E. coli c byn v m cho histidine trong mt hng. Trong peptide dn u operonthr ,c 11 nhm n v m cho threonine v isoleucine. T khi threonine l tincht cho isoleucine, kim sot s suy gim bao gm cho n v m cho chai axit amin ny. Khi ngun d tr mt acid amin trong trng thi thiuht, s kh khn cho ribosome trong vic tm mt tRNA mang acid aminc th v n chm dn li. Khi mt s n v m cho mt acid amin hitheo sau ln nhau, cc ribosome s tm thi dng li. Cc ribosome bao ph trnh t 1, loop 2 / 3 v loop kt thc s khng c to ra(Fig.11.16B). Cc RNA polymerase n phin m phn cn li camRNA.

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Hnh 11/16: Ribosome Ngn Cn S Hnh Thnh Ca Loop Kt Thc

S suy gim kim sot vic tng hp cc mRNA c hon thnhhoc khng pht trin. [ RNA polymerase khng hin th trong hnh ny,tht ng c ch suy gim.] (A) Vng dn u ca mRNA cha cc trn

t m ha cho peptide dn u v bn trnh t c th (1, 2, 3 v 4) m cth c cp baz hnh thnh cu trc kt cp b sung v cu trc loop(B) Khi thiu cc acid amin tng ng, cc ribosome tr hon ti vng 1,cho php cu trc pre-emptor hnh thnh v s phin m ca mRNA bng RNA polymerase tip tc. Lu rng peptide dn u khng c hothnh. (C) Khi c mt lng giu c ca cc acid amin tng ng, peptidedn u c thc hin v ribosome di chuyn n vng 2 mt cch nhanchng, cho php cc vng 3 v 4 to thnh loop kt thc. iu ny

ngn cn s ko di ca mRNA.Trong Bacillus, ribosomes khng phc tp v khng c peptide dn

u. D sao, vng dn u ca cc mRNA c bn trnh t c th kt c to ra hai cu trc xen k. Protein suy gim lin kt vi acid amin annghin cu. Trong s hin din ca cc acid amin, cc protein suy gimlin kt vo vng dn u mRNA v thc y s kt thc. Trong Bacillus

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vng dn u 5 ca mRNA catrp cha mt hot ng ca mi mt b ba UAG hoc GAG tch ra khi nhau ca hai hoc ba baz khc. Mmt tiu n v ca protein suy gim tryptophan (tryptophan attenuation protein (TRAP)) vi nhng lin kt, to thnh mt vng mi mt thnhvin (Fig.11.17). iu ny cho php hnh thnh thn quai kt thc v do gy ra s kt thc sm qu trnh phin m.

Riboswitches - RNA Tc ng Trc Tip Nh L Mt C Ch iuKhin

Mt trong nhng cu chuyn hp dn gn y trong sinh hc phn t c khm ph rng RNA c th thc hin nhiu chc nng m trc ngi ta tin rng cn phi c nhiu protein. Nh ta bit, Ribozymel phn t RNA c kh nng xc tc, tham gia vo phn ng ct ni RNAtng hp protein v sao chp trong virut. RNA i ngha v mt lot cc phn t RNA iu khin nh, chng hn nh siRNA c tham gia viu ha gen. Gn y nht, tm thy nhng phm vi ca RNA phtrc RNA thng tin, gi tt l riboswitches, c th trc tip tng tc v

nhng phn t nhv c th kim sots biu hin cagene. i a s ccriboswitches c tm thy trongvi khun v cho nnay n ch l thnghim trong vikhun v l bngchng cho s tnti hot ngriboswitch.

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Hnh 11/17: S suy gim bng protein lin kt RNA Khi tryptophan l c mt, n say sa lin kt vo protein suy gim

tryptophan. Nhng lin kt ny lm cho cu trc RNA thay i. Thay cu trc RNA to nn cu trc thn quai l nguyn nhn kt thc sm.

Mt s phn t RNA thng tin c th kim sot qu trnh dch m camnh thng qua cc vng riboswitch c lin kt vi cc phn t nh .

Protein suy gim: protein iu khin tham gia vo vic lm gim vlin kt vi vng khi u ca mRNA

Riboswitch: vng ca RNA thng tin trc tip nhn bit mt tn hiv kim sot qu trnh dch m bng mt trong hai cu trc

Tuy nhin, phn tch trong trnh t cho thy genomes ca mt snm v thc vt c cha nhng trnh t tng ng, hm trong chnchc chn cng c riboswitches.

Qu trnh sinh tng hp to ra sn phm chuyn ha nh axit amin vvitamin thng gy cm ng khi ngun cung cp sn phm chuyn hngn nhng c tt khi ngun d tr sn phm chuyn ha phong phCc gene cho qu trnh sinh tng hp nh vy thng c kim sot bcc cht c ch hoc bi s suy gim v c km nn phn ng litp trung cao cc sn phm chuyn ha nghin cu. Trong nhng trnhp ny, cc sn phm chuyn ha lin kt vi mt protein iu khin nh m t, chng hn nh ArgR repressor ca E. coli c lin kt viarginine, hoc s lm gim protein (tryptophan tryptophan attenuation protein (TRAP)) ca Bacillus c lin kt vi tryptophan.

Trong riboswitches, cc sn phm chuyn ha lin kt trc tip mtrnh t RNA ti u tn cng 5 ca RNA thng tin. V d, riboswitchthiamine ca E. coli c cha mt trnh t lin kt vi vitamin/ng yu tthiamine pyrophosphate vi tnh c th cao v c bit n nh l hpTHI. Tng t nh cc hp RFN ca riboflavin trong riboswitch Bacillussubtilis lin kt vi mononucleotide flavin. Khi cc vitamin ny c cungcp ngn nhng gen sinh tng hp c bt m khng c s can thip c bt k protein iu khin no. Ngc li, khi vitamin xut hin mc cao, cc gene c tt. Hin nay Riboswitches ang c bit n cho m

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Vi sinh vt phn t

s vitamin, mt s axit amin (methio chn v Lysine) v baz purine ccadenine v guanine.

Hnh 11/18: C ch ca Riboswitch Riboswitches lun phin gia hai cu trc: cu trc kt cp b sung

v cu trc loop ph thuc vo s c mt hoc vng mt ca tn hicht chuyn ha.

(A) Trong c ch suy gim, kt qu ca s c mt ca tn hiu chchuyn ha hnh thnh cu trc kt thc v qu trnh phin m khng th tip tc c. (B) Trong c ch c ch qu trnh dch m, kt qu ca sc mt ca cht chuyn ha dn n s cch ly trnh t Shine-Dalgarnodo ngn cn s dch m ca mRNA.

Lin kt ca ca cc sn phm chuyn ha ti nhng hp RNA thay i hnh dng ca ton b vng riboswitch. Riboswitches tn ti tronghai hnh dng lun phin khc nhau cu trc kt cp b sung v cu trcloop. iu ny ln lt kim sot s biu hin ca gen bi mt trong h

iu ha cp RNA36


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Vi sinh vt phn t

c ch lin quan, kt thc sm qu trnh phin m (tc l lm gim) hocc ch qu trnh dch m:

Trong c ch suy gim (Hnh 11.18A), vic riboswitch kim sotkhng bit c hay khng cc mRNA cho cc gen sinh tng hp s kt thcsm. Ti y cc riboswitch tch cc trnh t kt thc ra tn hiu ca nkhng c mt trong sn phm chuyn ha v qu trnh phin m tip tcKhi cc sn phm chuyn ha lin kt, cc riboswitch thay i hnh dngcho ph cho php mt s hnh thnh mt thn quai kt thc, l nguynnhn kt thc sm ca mRNA. Do vy, cc gene khng c biu hin.

Trong c ch c ch qu trnh dch m (Hnh 11.18B), vic riboswitchkim sot c hay khng c cc mRNA s c dch m. Khi khng c tnhiu bm gi sn phm chuyn ha trnh t Shine-Dalgarno lin kt t dvi RNA ribosome (rRNA) v qu trnh dch m c tin hnh. Khi ctn hiu bm gi sn phm chuyn ha, cc riboswitch tch trnh t ShineDalgarno ra v s dch m b ngn cn.

Riboswitches cng c th p ng cc iu kin vt l nh tri ngvi cc phn t nh. Cc RNA thermosoensor l mt loi c trng cariboswitch p ng nhit v kim sot mRNA dch m bng vitch trnh t Shine-Dalgarno ra. Vi nguyn l tng t nh trn, nhnghnh thnh mt trong hai cu trc kt cp b sung hoc cu trc loop phthuc trc tip vo nhit . nhit cao, mt trong nhng cu trc kcp b sung khng n nh v riboswitch chuyn i n cc dng nhit cao. Cc genrpoH ca E. coli tham gia vo cc phn ng sc nhit, nhc m t trong Chng 9. Ngoi nhng m t qu trnh iu ha , qutrnh dch mrpoH mRNA c ngn cn bi mt RNA thermosoensor nhit thp, nhng khi nhit tng ln qu trnh dch m c tip tCc gene khc ca qu trnh dch m c kim sot bi RNAthermosoensors bao gm mt s gen hot ha tham gia vo tnh c ca vkhun gy bnh chng hn nhYersiniav Listeria. Bn ngoi vt ch, ccgene c tt bng c ch qu trnh dch m. Bn trong vt ch l ng vc v mu nng khi nhit m p cc protein hot ha c biu hinCc protein hot ha sau tin hnh kch hot mt s gene khc linquan n tnh c ca vi khun.

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Vi sinh vt phn t

Riboswitches c th p ng vi tt nhit nh s tp trung cccht chuyn ha.

Documents

Chapter 8 _ Điều hoà ở mức độ RNA _ bài dịch phan văn nam