Translation repression by an RNA polymerase elongation complex

Summary Bacteriophage λ N and bacterial Nus proteins together with a unique site NUT in the leader of the early viral N gene transcript bind RNA polymerase (RNAP) and form a highly processive antitermination complex; N bound at NUT also represses N translation. In this study, we investigate whether N and NUT cause N translation repression as part of the antitermination complex by testing conditions that inhibit the formation of the N-modified transcription complex for their effect on N-mediated translation repression. We show that nus and nut mutations that in combination destabilize multiple interactions in the antitermination complex prevent N-mediated translation repression. Likewise, transcription of the nut-N region by T7 RNAP, which does not lead to the assembly of an effective antitermination complex when N is supplied, eliminates translation repression. We also demonstrate that a unique mutant β subunit of RNAP reduces N-mediated translation repression, and that overexpression of transcription factor NusA suppresses this defect. We conclude that the N-modified RNAP transcription complex is necessary to repress N translation.