The RecA Protein

Abstract

This chapter focuses on the bacterial RecA proteins, which have at least three major roles. The first function involves a direct participation in the central steps of recombination, via the DNA strand exchange activity. Second, RecA protein has a role in regulation. As a regulatory function, the RecA protein facilitates the autocatalytic cleavage of the LexA repressor and certain other proteins to induce the SOS response to DNA damage. Finally, the RecA protein participates in yet another type of repair process. Late in the SOS response, especially when DNA damage levels are particularly high and nonmutagenic DNA repair is insufficient to get replication restarted, a need arises to restart replication via lesion bypass. The known biochemical activities of the RecA protein parallel these cellular roles. These include binding to DNA, ATP hydrolysis, filament formation, DNA strand exchange, and the coprotease activity. The nucleation of RecA protein on single-stranded DNA (ssDNA) is slowed considerably if the DNA is bound by the Escherichia coli single-strand DNA-binding protein SSB. The capacity to promote uniquely unidirectional DNA strand exchange reactions, to bypass significant structural barriers, and to promote four-strand exchange reactions is so far unique to the bacterial RecA proteins, and all of these processes require ATP hydrolysis.