A mutation in the Escherichia coli rho gene that inhibits the N protein activity of phage λ

Abstract

Certain Escherichia coli rho mutations, exemplified by rho026, block the growth of phage λ by interfering with phage gene expression. The phage gene N, whose product suppresses transcription termination, appears to be expressed normally in the mutants, and the functional stability of the N protein is not affected. Our data suggest that these rho mutations allow transcription to terminate despite the presence of N. Other E. coli mutants displaying a similar phenotype (Nus-) fail to propagate wild-type λ but permit the growth of the λ variant λnin5, which has undergone a deletion of the λ terminator t(R2). The phenotype of the rho026 mutant differs: the growth of λ is only marginally improved by the nin5 deletion. Interestingly, N activity at rho-independent terminators is not inhibited by the mutations, whereas its ability to suppress rho-dependent terminators is markedly reduced. The relevance of this specificity in terms of models of N action is discussed.