Evidence for a λ transducing phage carrying the genes for the β and β′ subunits of Escherichia coli RNA polymerase

Complementation tests performed between the rifampicin resistance transducing phage λcI857s7drif d18 and a polar amber mutation in RNA polymerase affecting the synthesis of both the β and β′ subunits, show that this phage carries both of these genes. In contrast, a second rif transducing phage, λcI857s7drif d12, fails to complement the polar mutation, but does complement a non-polar amber mutation affecting the synthesis of only the β subunit. Synthesis of β and β′ in the strain containing λcI857s7drif d18 and the polar amber mutation proceeds at the normal rate, suggesting that this phage also carries the promoter region for this set of bacterial genes. Replication of the same lysogen after heat induction produces a moderate gene dosage effect on subunit synthesis.