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Bipolar DNA Translocation Contr ibutes to Highly Processive DNA Unwinding by RecBCD Enzyme Mark S. Dillingham .etal 280 37069-3 7077 銘銘銘銘 銘銘—銘銘銘 2005.11.29

Introduction

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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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Page 1: Introduction

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

Page 2: Introduction

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)

Page 3: Introduction
Page 4: Introduction

RecBCD Pathway

Page 5: Introduction

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

Page 6: Introduction

EXPERIMENTAL PROCEDURES

• DNA substrates-

• Proteins-

• Stopped-flow dye-displacement helicase assay-

• Conventional dye displacement helicase assay-

• SSB-binding coupled helicase assay-

Page 7: Introduction

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)

Page 8: Introduction

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

Page 9: Introduction

公式

D =the total of DNA endsE =total enzyme conc.

V =unwinding rateK d=the enzyme affinity to DNA

Page 10: Introduction

名詞介紹• Unwinding rate

• Unwind amplitude

• heparin

Page 11: Introduction

• 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

Page 12: Introduction
Page 13: Introduction

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)

Page 14: Introduction

• 加了 trap (heparin) 和使用了 SSB 的效果

• 低濃度的 Mg2+ 離子

Page 15: Introduction

• 對各種 DNA 尾端的接受度

Page 16: Introduction

整理

Page 17: Introduction
Page 18: Introduction

事先作 pre-bond 的動作 , 把 RecBK29QCD 先結合在 DNA 上

Page 19: Introduction

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.

Page 20: Introduction

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?

Page 21: Introduction

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

Page 22: Introduction

END