title: A comparison of the DNA binding and bending capacities and the oligomeric states of the immunity repressors of heteroimmune coliphages P2 and WPhi.
abstract: Bacteriophages P2 and WPhi are heteroimmune members of the P2-like family of temperate Escherichia coli phages. Temperate phages can grow lytically or form lysogeny after infection. A transcriptional switch that contains two con-vergent promoters, Pe and Pc, and two repressors regulate what life mode to enter. The immunity repressor C is the first gene of the lysogenic operon, and it blocks the early Pe promoter. In this work, some characteristics of the C proteins of P2 and WPhi are compared. An in vivo genetic analysis shows that WPhi C, like P2 C, has a strong dimerization activity in the absence of its DNA target. Both C proteins recognize two directly repeated sequences, termed half-sites and a strong bending is induced in the respective DNA target upon binding. P2 C is unable to bind to one half-site as opposed to WPhi, but both half-sites are required for repression of WPhi Pe. A reduction from three to two helical turns between the centers of the half-sites in WPhi has no significant effect on the capacity to repress Pe. However, the protein-DNA complexes formed differ, as determined by electrophoretic mobility shift experiments. A difference in spontaneous phage production is observed in isogenic lysogens.
authors.affiliation: Department of Genetics, Microbiology and Toxicology, Stockholm University, S-106 91 Stockholm, Sweden.
authors.forename: Alexandra
authors.initials: A
authors.lastname: Ahlgren-Berg
authors.forename: Petri
authors.initials: P
authors.lastname: Henriksson-Peltola
authors.forename: Wilhelmina
authors.initials: W
authors.lastname: Sehlén
authors.forename: Elisabeth
authors.initials: E
authors.lastname: Haggård-Ljungquist
mesh_terms: D000595:Amino Acid Sequence; D017901:Bacteriophage P2 / Q000235:genetics* / Q000254:growth & development; D001665:Binding Sites; D003090:Coliphages / Q000235:genetics* / Q000254:growth & development; D004247:DNA / Q000737:chemistry / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000378:metabolism; D019281:Dimerization; D015967:Gene Expression Regulation, Viral; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D009875:Operator Regions, Genetic; D011401:Promoter Regions, Genetic; D012097:Repressor Proteins / Q000737:chemistry / Q000378:metabolism*; D014764:Viral Proteins / Q000737:chemistry / Q000378:metabolism*
chemical_list: C117790:C protein, Enterobacteria phage P2; D004268:DNA-Binding Proteins; D012097:Repressor Proteins; D014764:Viral Proteins; D004247:DNA