The recA Gene Product from E. coli. Binding to Single-Stranded and Double-Stranded DNA

Abstract

The recA gene product from E. coli plays a central role in two major functions which are essential to the bacterium life: i) it catalyzes general genetic recombination by promoting DNA strand exchange reactions. In vitro it has been shown that RecA protein catalyzes the formation of duplex DNA from complementary single-stranded molecules (annealing), the assimilation of linear single-strands into duplex circular DNA to form D-loops, the pairing of gapped circular DNA with either superhelical or nicked circular DNA, the complete exchange of strands between full length linear duplex and homologous circular single-stranded DNA. D-loop formation requires ATP but not its hydrolysis whereas extension of an heteroduplex via branch migration requires ATP hydrolysis and proceeds with a unique polarity (for review see references 1,2); ii) the recA gene product plays a crucial role in DNA repair. When DNA replication is perturbed either as a consequence of damages induced in DNA by physical (radiations) or chemical agents, or by an alteration of the replication fork, a series of genes called the “SOS genes” are derepressed. These genes are under the control of a common repressor, the lexA gene product, which is cleaved by the RecA protein. This proteolytic activity of the RecA protein is induced when it binds to single-stranded DNA in the presence of ATP, even though ATP hydrolysis is not required for the cleavage reaction (for review see reference 3).