Multilevel regulation of bacteriophage lambda lysogeny by the E. coli himA gene.

Previous experiments have shown that the himA gene of E. coli specifies a protein that is required for bacteriophage lambda integration. lambda Forms clear plaques on himA mutants indicating a possible additional defect in the establishment of repression. We have tested the effects of a himA mutation on the establishment and maintenance of lambda repressor (cl) synthesis and on the synthesis of Int protein. The rate of synthesis of cl and Int after infection by lambda is severely reduced in a strain carrying a himA gene deletion. Synthesis of Int or repressor can occur in the himA- strain if the phage carry constitutive promoters for either the int gene or the cl gene. Maintenance of repression is unaffected by himA mutations as judged by repressor-stimulated transcription of PM fused to the lacZ gene. These results indicate that the himA gene participates in the regulation of the promoter sites specific of the establishment of lysogeny: PE for cl synthesis and PI, for Int production. Since the himA gene product is required also for lambda site-specific recombination, it appears that the himA gene regulates lambda lysogeny at several levels. I discuss the significance of this multilevel regulation to lambda development.