title: Role of E.coli NusA in phage HK022 Nun-mediated transcription termination.
abstract: The 109 amino acid residue Nun protein expressed from prophage HK022 excludes superinfecting phage lambda by arresting transcription on the lambda chromosome near the lambdanut sites. In vitro, the Nun N terminus binds to nascent lambdanutRNA, whereas the C terminus interacts with RNA polymerase and DNA template. Escherichia coli host factors, NusA, NusB, NusE (S10), and NusG, stimulate Nun-arrest. NusA binds the Nun C terminus and enhances formation of the Nun-nutRNA complex. Because of these in vitro activities of NusA, and since a nusA mutation (nusAE136K) blocked Nun in vivo, we assumed that NusA was required for Nun activity. However, using a nusAts strain, we find that NusA is required for termination at nutR but not at nutL. Furthermore, nusAE136K is dominant to nusA(+) for Nun-arrest, both in vitro and in vivo. NusAE136K shows increased affinity for Nun and, unlike NusA(+), can readily be recovered in a ternary complex with Nun and nutRNA. We propose NusAE136K suppresses Nun-arrest when it is a component of the transcription elongation complex, perhaps, in part, by blocking interactions between the Nun C terminus and RNA polymerase and DNA. We also find that in contrast to Nun-arrest, antitermination by lambda N requires NusA.
authors.affiliation: Department of Biochemistry and Molecular Biophysics, Columbia University Medical Center, New York, NY 10032, USA.
authors.forename: Hyeong C
authors.initials: HC
authors.lastname: Kim
authors.forename: Robert S
authors.initials: RS
authors.lastname: Washburn
authors.forename: Max E
authors.initials: ME
authors.lastname: Gottesman
mesh_terms: D025523:Bacteriophage HK022 / Q000235:genetics / Q000378:metabolism*; D010582:Bacteriophage lambda / Q000235:genetics / Q000378:metabolism; D012321:DNA-Directed RNA Polymerases / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism*; D046911:Macromolecular Substances; D008957:Models, Genetic; D009154:Mutation; D010445:Peptide Elongation Factors / Q000235:genetics / Q000378:metabolism*; D013728:Terminator Regions, Genetic; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic; D035602:Transcriptional Elongation Factors; D014764:Viral Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D029968:Escherichia coli Proteins; D046911:Macromolecular Substances; C073501:Nun protein, Enterobacteria phage HK022; D010445:Peptide Elongation Factors; D014157:Transcription Factors; D035602:Transcriptional Elongation Factors; D014764:Viral Proteins; C068727:nusA protein, E coli; D012321:DNA-Directed RNA Polymerases