SOS induction and autoregulation of the himA gene for site-specific recombination in Escherichia coli.

Abstract

The himA gene of E. coli controls the lysogenization of bacteriophage .lambda. at the level of catalysis of site-specific recombination and expression of the .lambda. int and cI genes required for lysogenic development. The regulation of himA was analyzed by monitoring .beta.-galactosidase synthesis from a lacZ gene inserted into the himA gene and detection of radioactive HimA protein after fractionation by 2-dimensional gel electrophoresis. himA- mutations produce enhanced expression of the himA gene, indicating that HimA protein controls its own synthesis. The himA gene is also induced by treatment of cells with UV or mitomycin C, suggesting control by the inducible DNA repair (SOS) system regulated by the LexA and Rec proteins. Regulation of himA follows the pattern expected for a typical SOS gene: constitutive high expression in mutants that have inactive LexA or the altered RecA conferred by the recA441 (tif1) mutation and low noninducible expression in a mutant that has a deleted recA gene. The himA gene is apparently a component of the inducible SOS response, repressed by LexA and induced by the capacity of activated RecA to cleave LexA. HimA may be subject to SOS induction because it functions as an acquisitionase for new genetic material. HimA may be of special use under conditions of impaired capacity for growth of the bacterial population.