Preferential cleavage of phage λ repressor monomers by recA protease

Abstract

Expression of phage lytic functions in λ lysogens of Escherichia coli is prevented by phage repressor, which binds to specific operator sequences on the prophage DNA. Phage induction accompanies the expression of an entire set of ‘SOS functions’, which occur when host DNA is damaged or DNA synthesis is interrupted. In these conditions, λ repressor is thought to be inactivated by recA protease, thereby leading to expression of phage lytic functions¹. We have now characterized the repressor from a λ mutant, ind^s-1, which, as prophage, is more easily induced than wild-type phage by a weak inducing treatment². At high concentrations, λind^s-1 repressor differs from wild-type repressor in two ways: whereas wild-type repressor forms dimers and becomes relatively resistant to the recA protease, a much greater proportion of λind^s-1 repressor remains monomeric and the protein remains sensitive to the protease. These findings support previous indications³ that repressor monomers are the preferred substrate for protease, both in vivo and in vitro.