Escherichia coli nusG mutations that block transcription termination by coliphage HK022 Nun protein

Abstract

The Escherichia coli nusG gene product is required for transcription termination by phage HK022 Nun protein at the λ nutR site in vivo. We show that it is also essential for Nun termination at λ nutL. Three recessive missense nusG mutations have been isolated that inhibit termination by Nun at λ nutR. The mutations are ineffective in a λ pL nutL fusion, even when λ nutR replaces λ nutL. The mutant strains support λ growth, indicating that λ N antitermination activity is not impaired. Transcription arrest by Nun in vitro is stimulated by NusG protein at both λ nutR and λ nutL. Mutant NusG protein fails to enhance transcriptional arrest by Nun at either site. The mutant protein, like the wild-type protein, suppresses transcriptional pausing by RNA polymerase and stimulates Rho-dependent termination. These results imply that the role of NusG in Nun termination may be distinct from its roles in other transcription reactions.