Translational Polarity of a Mutation in the Initiator AUG Codon of the Λ cI Gene

Abstract

ABSTRACT A PRM-cI-lacZ fusion inserted into the b2 region of bacteriophage λ was used to isolate mutations affecting expression of both the λ cI gene and the lacZ gene. One such mutation, a change in the cI initiator codon from AUG to AUA, reduces immunity of a λ prophage to superinfection, and causes a 60-70% reduction in β-galactosidase synthesis, even when repressor is supplied in trans. The effect of the mutation on lacZ gene expression is eliminated in a rho  - bacterial strain, and the mutation has no effect on transcription initiated at PRM in vitro. Therefore, the effects of the mutation are due to premature ρ-dependent termination of transcription in the absence of translation of the cI gene, as if the mutation were a nonsense polar mutation.