title: The activity of the CIII regulator of lambdoid bacteriophages resides within a 24-amino acid protein domain.
abstract: The CIII protein of lambdoid bacteriophages promotes lysogeny by stabilizing the phage-encoded CII protein, a transcriptional activator of the repressor and integrase genes. We have isolated a set of missense mutations in the cIII gene of phage lambda and of phage HK022 that yield inactive CIII proteins. All the mutations are located in the relatively conserved central region of the protein. A comparative analysis of the CIII protein sequence in lambda, HK022, and the lambdoid bacteriophage P22 leads us to suggest that this central region assumes an amphipathic alpha-helical structure. This part of the lambda cIII gene was cloned within a fragment of the lacZ gene (the alpha-complementing fragment). The resulting fusion protein displays CIII activity. Mutations that yield a nonfunctional fusion protein map within its CIII moiety. These results indicate that the central portion of the CIII protein is both necessary and sufficient for CIII activity.
authors.affiliation: Department of Molecular Genetics, Hebrew University-Hadassah Medical School, Jerusalem, Israel.
authors.forename: D
authors.initials: D
authors.lastname: Kornitzer
authors.forename: S
authors.initials: S
authors.lastname: Altuvia
authors.forename: A B
authors.initials: AB
authors.lastname: Oppenheim
mesh_terms: D000595:Amino Acid Sequence; D010582:Bacteriophage lambda / Q000235:genetics* / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D008969:Molecular Sequence Data; D009154:Mutation; D010957:Plasmids; D011487:Protein Conformation; D012689:Sequence Homology, Nucleic Acid; D014157:Transcription Factors / Q000235:genetics*; D014760:Viral Fusion Proteins / Q000378:metabolism; D014764:Viral Proteins
chemical_list: D014157:Transcription Factors; D014760:Viral Fusion Proteins; D014764:Viral Proteins; C054615:cIII protein, Bacteriophage lambda