Interactions of the λ cllls1 and the E. coli hfl-1 mutations

Abstract

Following infection of Escherichia coli K-12, the λ cII and cIII proteins stimulate a high level of synthesis of the λ repressor (the product of the cI gene). This stimulation is necessary for efficient lysogenization. The cII protein may act directly to stimulate transcription of cI, while the cIII protein probably acts by blocking a host function called hfl, which is capable of inhibiting cII. With a DNA filter binding assay for the λ repressor, I show here that (1) λ cIII + and cIII − each produce more repressor after infection of a host deficient in the hfl function ( hfl −) than after infection of the hfl + parent; (2) the ratio of repressor synthesized by a λ mutant with enhanced cIII activity (λ cIIIs) to that produced by λ wild type is lower in an hfl − strain than in an hfl + strain. These results support the idea that hfl and cIIIs both act by increasing the activity of the cII protein.