1. The Role of RecA in DNA Replication Hazem Dawoud http://www.callutheran.edu/BioDev/omm/reca/recamast.htm

2. Outline * introduction. * RecA binding sites. * RecA functions and activities. * SOS response. * TLS * RecA filament formation on DNA. * Repair of a collapsed replication fork by RecA protein.

3. DNA replication

4. DNA Replication

5. RecA protein : 38 kilodalton polypeptide. identified in E. coli by Clark and Margulies in 1965. DNA repair and maintenance. Class of homologous DNA repair protein. More than one DNA binding site. DNA dependent ATPase : allosteric enzyme.

6. Nature Reviews Molecular Cell Biology 8, 127-138 (February 2007) | RecA Binding sites: DNA binding sites. ATP binding sites

7. RecA protein functions: Repair of stalled replication fork double-strand break repair general recombination induction of the SOS response SOS mutagenesis Annu Rev Microbiol. 2003;57:551-77. Cox MM. Promotes mutagenic Trans- Lesion Synthesis by polV.

8. Activities of Escherichia Coli RecA: a-Strand invasion reaction b- a three-strand- exchange reaction C-a four-strand- exchange reaction. d-The replication fork regression reaction e- the RecA coprotease function. f- stimulation of translesion -DNA- replication activity of DNA pol 5 Nature Reviews Molecular Cell Biology 8, 127-138 (February 2007) |

9. In non-induced growth conditions, the LexA repressor binds to SOS-controlled promoters, limiting or preventing their action. RecA filaments formed at sites of damage activate the autocleavage of the LexA repressor, allowing SOS gene expression. SOS induction is reversed when damages are repaired. PLoS Biol. 2005 July; 3(7): e255. Bénédicte Michel The SOS Respose:

10. TLS : Trans-Lesion SynthesisDNA damage tolerance process Involves switching out regular DNA pol with specialized trans-lesion pol. Low fidelity on the undamaged template. PCNA, proliferating cell nuclear antigen, provides a platform for TLS Pol.

11. recombination repair

12. 01/09/12 Cox Nature Reviews Molecular Cell Biology 8, 127–138 (February 2007) | doi:10.1038/nrm2099 Assembly of RecA filaments:

13. RecA protein Filament Formation on DNA. Critical Reviews in Biochemistry and Molecular Biology, 42:41–63, 2007, Michael M. Cox RecA protein filaments are generally formed in two distinct phases, nucleation and extension. Extension proceeds largely in the 5 to 3 direction, and cancontinue readily into any adjacent duplex DNA.

14. Repair of a collapsed replication fork. RecA bind to ss DNA and catalyze hyperdization. RecA catalyze invasion of duplex DNA.

15. Summary * RecA protein is DNA binding protein with multiple activiries. * RecA protein polymerize to form nucleoprotein filament. *RecA protein promotes mutagenic TLS by pol V. * RecA protein induces the SOS respose. * RecA promotes strand invasion to initiate recombination. * RecA protein repair of stalled replication fork.

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