A mechanism for transcription antitermination by the phage 21 N antiterminator

Date of Completion

January 1998


Biology, Genetics|Biology, Microbiology




The N antiterminators from the bacteriophage λ, P21, and P22, together with RNA encoded by their cognate nut sites, alter RNA polymerase (RNAP) such that the transcription elongation complex can now bypass transcription terminators. Presently, it is not clear how these proteins allow RNAP to ignore the commands issued by transcription terminators. Studies with the N antiterminator (Nλ) from λ bacteriophage suggest that its direct interaction with a subunit(s) of RNAP transforms RNAP to a termination-resistant state. ^ We present genetic data suggesting that the molecular mechanism of antitermination by the N antiterminators may in part differ. In contrast to Nλ, a small amino-terminal peptide from P21 bacteriophage N antiterminator (N21) apparently does not activate RNAP through contact to termination-resistant state. Several observations lead us to believe that the amino-terminus of N21 signals RNAP through nut21. The P21 nut site, most likely in its RNA form through association with RNAP, confers an ability to readthrough terminators. ^