ESCHERICHIA-COLI MUTATIONS THAT BLOCK TRANSCRIPTION TERMINATION BY PHAGE HK022 NUN PROTEIN

The nun gene product of the lambdoid coliphage HK022 provokes premature transcription termination at, or near, the phage λ nut sites. Termination by Nun and antitermination by λ N protein both require the nut sites and Escherichia coli NusA, NusB and NusE proteins. To characterize further the host requirements for Nun termination, we selected host mutations that blocked termination at λ nutR. In addition to mutations in nusA, nusB and nusE, we obtained mutations in rpoC, encoding the RNA polymerase β′ subunit. The nusA and rpoC mutations suppressed Nun termination but not antitermination by λ N function. The mutations antagonized Nun only at λ nutR; termination at λ nutL occurred in all the mutant strains. Thus, nutL is not functionally equivalent to nutR. We conclude that the host requirements for Nun termination overlap but are not identical with those for N antitermination, and, in particular, that the β′ subunit of RNP may be Nun-specific. © 1991.