Role of RecA in DNA replication

Yadi Zhou2013.12.05

RecA protein

• 38 kiloDalton• Essential for the repair and maintenance of DNA• A RecA structural and functional homolog has been

found in every species• Homologous protein in Homo sapiens is RAD51

• Important enzyme in homologous recombination• Induce SOS response

Structure

RecA filament

RecA-dsDNA

Homologous recombination

Homologous recombination

SOS response

• E. coli strains deficient in RecA are useful

• Potential drug target

References

• http://www.callutheran.edu/BioDev/omm/reca/recamast.htm• http://en.wikipedia.org/wiki/RecA• Nature Reviews Molecular Cell Biology 8, 127-138

(February 2007)• http://www.callutheran.edu/BioDev/omm/reca/

recamast.htm• Nature 453, 463-466(22 May 2008)

Thank you!

Mechanisms of RecA DNA Repair

Vivian LesendeDecember 5, 2013

BIOS 7200

• Can arrest replication --- deletions/genomic rearrangements, point mutations, lethality• Many types of lesions can inhibit normal

progression of replication forks-UV radiation – cis, syn-cyclobutane pyrimidine dimer (CPD) & pyrimidine-6-4-pyrimidone photoproduct (6-4 PP)

DNA Damage

• RecA functions to recover replication forks in several different ways

-acts as transactivator for upregulating over 40 genes (SOS response)-protects single stranded DNA from degradation while replication is arrested-promotes recombination repair

RecA Functions

• LexA -- repressor binds to a 20 bp consensus sequence in operator region in DNA-damage inducible genes• RecA bound to damaged single stranded DNA

causes autocatalytic cleavage• Increases transcription of genes involved in SOS

Response

SOS Response

• Genes that function to remove lesions and restore replication• uvrA & uvrB -- recognize UV-induced lesions• ydjQ (cho) -- incision step for excision repair• polB, dinB, umuC & umuD – DNA polymerases Pol II,

PolI V, Pol V

Genes Involved in SOS Response

SOS Response

Courcelle & Hanawalt. Annu. Rev. Genet. 2003. 37:611-46

• RecA maintains structure of replication forks until replication resumes• Allows for nucleotide excision repair to occur• recA mutants have high sensitivity to UV-light –

“rec-less” degradation

Prevention of Degradation of Single-Stranded DNA of Replication Forks

Prevention of Degradation of Single-Stranded DNA of Replication Forks

Courcelle & Hanawalt. Annu. Rev. Genet. 2003. 37:611-46

• “postreplication repair” or “daughter-strand gap repair”• RecA promotes recombination as an alternative to

excision repair – does not remove lesions from DNA• Typically only occurs if previous mechanisms have

failed

Recombination Recovery

Recombination Recovery

Courcelle & Hanawalt. Annu. Rev. Genet. 2003. 37:611-46

• J. Courcelle & P. C. Hanawalt. RecA-Dependent Recovery of Arrested DNA Replication Forks. Annu. Rev. Genet. 2003. 37:611-46

References