Role of Rec A in DNA
Replication
Group 3
Salient Features of Rec A
• Rec A protein plays an important role in homologous recombination.
• Rec A is the molecule present in E.coli. Its homologs are found throughout
archaeans and eukaryotes.
• Rec A is instrumental in bringing about the SOS response of cells which have
accumulated considerable amounts of single stranded DNA breaks. The SOS
response comes directly after Nucleotide Excision Repair (NER).
• Can be used in colorimetric assays to test genotoxicity of chemicals.
Point of Interest in Rec A
• Rec A autocatalytically cleaves the Lex A repressor bound to the regulatory region
of SOS genes (SOS Box) and recruits DNA Polymerase II, IV and V to repair ssDNA
damage.
• Since these DNA Polymerases show less fidelity, this often leads to the
incorporation of wrong bases giving rise to mutations that may lead to cancer.
Homologs of Rec A Across Evolutionary
Groups
• Table 1. Proteins involved in different stages to DNA Replication and their
variations.
Collapsed Replication Fork Repair
Molecular Cell Biology, Seventh. Ed, Lodish et. al
Double
Stranded
Break
Repair
Figure 4-42, Molecular Cell Biology, Seventh. Ed, Lodish et. al
More Roles of RecA
Motoring along with the bacterial RecA protein. M. Cox, Nature Reviews (2007)
Strand
Exchange
Motoring along with the bacterial RecA protein.
M. Cox, Nature Reviews (2007)
Sequence of Multiple Strand Exchange
Motoring along with the bacterial RecA protein. M. Cox, Nature Reviews (2007)
Importance
• The filament provides binding sites for three DNA strands. For DNAstrand exchange that involves a single strand and a homologous
duplex  recombination
• Has an effect in recombinational DNA repair of replication forks and
facilitates conjugation in bacteria and meiotic recombination in
eukaryotes.
General mechanism for recombination and
Rec A action
• Two dsDNA molecules exchange segments of DNA at sites through
breakage and rejoining of strands, leading to recombinant
chromosomes with new combinations of alleles.
• The RecA protein is a critical enzyme in this process, as it catalyzes the
pairing of ssDNA with complementary regions of dsDNA.
Detail Rec A mechanism of action:
• Not mediated by ATP hydrolysis:
• Three strand exchange reaction in either direction, causing a D loop
formation.
• Mediated by ATP hydrolysis:
• Unidirectional DNA-strand exchange: 5′→3′ direction relative to the strand
that is first bound by the RecA filament.
• DNA-strand exchange through a barrier: it allows the bypass of significant
barriers in one of the DNA substrates.
• Four-strand exchanges: 5′→3′ direction relative to the ssDNA in the gap
where the reaction was initiated.
• Indirect helicase reaction.
• Fork regression: RecA assembles on a gap in the leading strand can lead to
the formation of a Holliday junction.
Rec A is also used in biotechnology
References
• http://www.callutheran.edu/BioDev/omm/reca/recamast.htm
• Rice et al. 2001, Encyclopedia of Life Sciences
• Costes et al. 2012, biomolecules