Lambda Repressor Inactivation: Properties of Purified Ind- Proteins in the Autodigestion and RecA-mediated Cleavage Reactions

Under physiological conditions, lambda repressor can be inactivated in vivo or in vitro by RecA-mediated cleavage of the polypeptide chain. The repressor protein is thought to cleave itself, with RecA acting to stimulate autodigestion. ind- repressor mutants are resistant to RecA-mediated inactivation in vivo. In this paper, we report the purification of 15 ind- repressor proteins and the behaviors of these proteins in the RecA-mediated and autodigestion cleavage reactions. None of these proteins undergoes substantial RecA-dependent cleavage. However, eight mutant proteins autodigest at the same rate as wild-type repressor, six mutants do not autodigest or autodigest slower, and one mutant autodigests faster than wild-type. We discuss these results with respect to repressor structure and RecA-binding, and suggest possible roles for the RecA protein in the cleavage reaction.