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Bipolar DNA Translocation Contributes to Highly Processive DNA Unwinding by RecBCD Enzyme Mark S. Dillingham .etal 280 37069-37077 銘傳生科 學生 — 朱祐頡 2005.11.29. Introduction. 研究動機 :double-stranded breaks RecBCD=RecB+RecC+RecD RecB 從 3’ 端開始 unwinding RecD 從 5’ 端開始 unwinding - PowerPoint PPT Presentation
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Bipolar DNA Translocation Contributes to Highly Processive
DNA Unwinding by RecBCD Enzyme
Mark S. Dillingham .etal 280 37069-37077
銘傳生科學生—朱祐頡 2005.11.29
Introduction
• 研究動機 :double-stranded breaks• RecBCD=RecB+RecC+RecD• RecB 從 3’ 端開始 unwinding RecD 從 5’ 端開始 unwinding 都需要 ATP(RecC)• Bipolar DNA 的描述• Chi sequence (5’-GCTGGTGG)
RecBCD Pathway
實驗設計• 因為 RecB,RecD 有許多共同點 weak helicase , nuclease, contain SF-1, , ATPase….RecBCD, RecBK29QCD, RecBCDK177Q
(ATP 的利用有關 ) 實驗的目的 : Highly Processive DNA Unwinding
EXPERIMENTAL PROCEDURES
• DNA substrates-
• Proteins-
• Stopped-flow dye-displacement helicase assay-
• Conventional dye displacement helicase assay-
• SSB-binding coupled helicase assay-
DNA substrates and Proteins
• PBR322 4-base 5′ overhangs
2-base 5′-overhangs
blunt ends
4-base 3′overhangs
No Chi sequences andλ phage DNA also
• RecBCD, RecBK29QCD, RecBCDK177Q and single-stranded DNA binding protein (SSB)
Stopped-flow dye-displacement helicase assay-
Trisacetate ,magnesium,DDT, Hoechst33258 dye and SSB
加入 2mM 的 ATP, 反應開始進行
另外作一個相同的時驗中 , 加入了 Heparin
DNA 上的螢光標記 使我們知道 DNA 上的 unwinding 的程度
公式
D =the total of DNA endsE =total enzyme conc.
V =unwinding rateK d=the enzyme affinity to DNA
名詞介紹• Unwinding rate
• Unwind amplitude
• heparin
• 圖 a 為 pre-bond 的情況討論 Heparin 的影響
• 圖 b 上圖為 pre-bond
下圖為非 pre-bond
Conventional dye displacement helicase assay- SSB-binding coupled helicase assay-
• Tris-acetate magnesium acetate, Hoechst 33258, SSB, and DTT.
Tris-acetate magnesium acetate, SSB, and 1 mM DTT, ATP
標準化 :
PBR322 plasmid and λ DNA
No protein (0% unwinding)Heat-denatured DNA(100% unwinding)
λ DNA.
No protein (0% unwinding)Heat-denatured DNA(100% unwinding)
• 加了 trap (heparin) 和使用了 SSB 的效果
• 低濃度的 Mg2+ 離子
• 對各種 DNA 尾端的接受度
整理
事先作 pre-bond 的動作 , 把 RecBK29QCD 先結合在 DNA 上
RESULTS
• Monitoring rapid unwinding of DNA by RecBCD using a stopped-flow dye-displacement
assay.• Mutation of helicase motif I in either RecB or Re
cD reduces the observed rate and amplitude of plasmid unwinding catalyzed by the RecBCD holoenzyme.
• The RecBK29QCD enzyme will only initiate unwinding from a short 5′- ssDNA overhang structure.
• Mutation of helicase motif I in either RecB or RecD severely reduces processivity of translocation by RecBCD.
DISCUSSION
• Rates of RecBCD-catalyzed DNA
unwinding: Which DNA motor is faster?
• Implications for general models of SF1
helicase activity.
• Why does RecBCD enzyme employ a
bipolar DNA translocation mechanism?
Conclusion
• 針對了 RecB ,RecD 這兩個 motor 的討論 對 Highly Processive DNA Unwinding
• 影響 RecBCD 的因子 作用在突變的 protein 上
• 親合性的討論及對尾端的接受度
END