Two mutations that alter the regulatory activity of E. coli recA protein

The Escherichia coli recA gene product is both a direct participant and a central regulatory element in important processes of DNA repair, including one that is probably responsible for all radiation mutagenesis and some chemical mutagenesis. It has the direct function of catalysing pairing of single-stranded DNA to a homologous region in duplex DNA, a reaction thought to be fundamental to genetic recombination. This activity of recA protein probably contributes to DNA repair by promoting recombination between damaged DNA molecules. We have shown that recA protein also has a regulatory function, mediated by its ability to destroy repressors and possibly other proteins by proteolytic cleavage, leading to the induction of certain genes; these include recA itself, regulated by the lexA gene product, other genes probably involved in DNA repair, some of which are also regulated by the lexA gene product, and the early genes of temperate bacteriophages, which are regulated by their repressors, recA protein is activated to cleave repressors in vitro by interaction with ATP (or the ATP analogue ATP-gamma S) and a polynucleotide such as single-stranded DNA, probably the same interaction that initiates the strand-pairing reaction. We have proposed that recA protein is also activated to attack repressors in vivo when it interacts with single-stranded DNA; DNA-damaging treatments such as UV-ray irradiation would thereby invoke the recA-dependent functions of recombination, repair, mutagenesis and prophage induction. As further evidence that the proteolytic activity of recA protein is responsible for its regulatory function, we show here that the ability of two mutationally altered recA proteins to cleave phage lambda repressor correlates with the ability of the mutant cells to induce prophage.