Interference with phage lambda cro gene function by a colicin-tolerant Escherichia coli mutant

An Escherichia coli mutant which was originally isolated as colicin tolerant and is defective in a membrane protein, alters the regulation of bacteriophage λ with a strong preference to lysogeny over the lytic pathway. Genetic and biochemical studies suggest that the λ cro antirepressor, a regulator acting in the decision between lysis and lysogeny, is unable to function in this host. λcro⁺ behaves in several respects as λcro^- when infecting this host. Thus cI repressor synthesis is not shut off, exonuclease production is not turned off, and defective lysogens cannot maintain a nonimmune state. Host revertants show both the reappearance of the membrane protein missing in the mutant and reversion with respect to λ regulation. It is suggested that cro gene function is regulated by association of λ DNA and the bacterial membrane.