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1. Welcome! • 班级：生物学基地班 • 姓名：陈浩 • 学号：200431060028

2. What is the function of the homologous recombination? How does the homologous recombination carry on? Chapter10 Homologous Recombination at the Molecular Levels

3. Key steps of homologous recombination • Alignment of two homologous DNA molecules • Introduction of breaks in the DNA • Formation of initial short regions of base pairing between the two recombination • Movement of the Holliday junction • Cleavage of the Holliday junction

4. The Holliday Model Double-strand Break Repair Model Models for Homologous Recombination

5. The Holliday Model • A nick is introduced to each of the double strand at an identical location • The Holliday junction that generated by strand invasion moves along the DNA by branch migration • The Holliday junction is resolved by the cutting the DNA strands near the site of the cross

6. Holliday model through the steps of branch migration

7. Holliday junction cleavage

8. Double-strand Break Repair Model • The introduction of the DSB in one of the two DNA molecules • DNA-cleaving enzyme degrades the broken DNA molecules to generate regions of single-strand DNA • The ssDNA tails invade the unbroken homologous DNA duplex • The two Holliday junctions move by branch migration and ultimately are resolved to finished recombination

9. DSB repair model for homologous recombination

10. Damage in the DNA template leads to DSB formation during DNA replication

11. In the Prokaryotes:The RedBCD Patchway needs RecA,RecBCD, RuvAB, RuvC to catalyze the biochemistry steps of recombination In the Eukaryotes:The Homologous Recombinationis completed by Dcm1,Spo11,MRX. Enzymatic Mechanisms of Recombination

12. The BCD Pathway • The RecBCD Helicase/Nuclease Breoken DNA Molecules for Recombination • RecA Protein Assembles on Single-Stranded DNA and Promotes Strand Invasion • RuvAB Complex Recognize Holliday Junctions and Promotes Branch Migration • RuvC Cleaves Specific DNA Strands at the Holliday Junctions to Finish Recombination

13. Steps of DNA Processing by RecCD

14. Substrates for RecA strand exchange

15. The structure of RuvA-DNA complex and schematic model of the RuvAB complex bound to Holliday junction DNA

16. The structure of RuvC resolvase and schematic model of the RuvC dimer bound to Holliday junction DNA

17. Homologous Recombination in Eukaryotes ⅠProgrammed Generation of Double-Stranded DNA Breaks Occur during Meiosis ⅡMRX Protein Processes the Cleaved DNA Ends for Assembly of the RecA-like Strandd-Exchange Protein ⅢDmc1 Is a RecA-like Protein that Functions in Meiotic Recombination ⅣMany Proteins Function Together to Promote Meiotic Recomabintion

18. DNA dynamics during meiosis

19. Mechanism of cleavage by Spo11

20. Overview of meiotic recombination pathway

21. Each structure shown is a replicated, double-stranded DNA molecule called a chromatid. The pairs are called sister chromatids,and recombination mediated by Dmc1 occurs between nonsister pairs.

22. Mating-Type Switching • Mating-Type Switching Is Initiated by a Site-Specific Double-Strand Break • Mating-Type Switching Is Gene Conversion Event, Not Associated with Crossing Over

23. Genetic loci encoding mating-type information

24. Recombination model for mating-type switching :synthesis-dependent strand annealing (SDSA)

25. Genetic Consequence of the Mechanism of Homologous Recombination • The repair of several types of DNA damage • Enhancement of the genetic diversity in a population • The control of the gene expression • Gene conversion

26. OUTLINE • Key Concepts: Holliday model ,DSB model, RecBCD Pathway,Mating-Type Switching • Critical Protein: Dcm1,Spo11,MRX,RecA,RecBCD,RuvAB, RuvC.

27. Thank You!!!