Amber mutants in the O gene of bacteriophage λ are not efficiently complemented in the absence of phage N function

Abstract

Mutants of bacteriophage λ carrying mutations in the replication genes O and P are complemented efficiently by O + P + phages under normal conditions of lytic growth. When analogous complementation tests are performed under N − conditions, however, P − mutants are efficiently complemented but Oam29 is not. This defect in O complementation is alleviated by the mutation of ri 5b c and is not observed with the nonamber mutation Ots21. These and other data suggest that, in the absence of N function, the Oam29 mutations exerts a cis effect on the development of genomes carrying it. The most likely explanation for this cis effect is that the amber codon interfers with transcriptional activation of λ DNA replication.