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

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.

The genetic locations oftraO, finPandtra-4 on theE. coliK12 sex factor F

SUMMARYUsing a series of Hfr and F prime deletion strains, the F transfer inhibition genefinPhas been mapped betweenoriandtraJ. Marker rescue experiments with the Hfr deletion strains further showed thattraO, the site of action of the transfer inhibitor, is located immediately to the left of, or possibly within,traJ, and that the polar mutationtra-4lies intraK.