Immunity repressor of bacteriophage P2. Identification and DNA-binding activity

The product of gene C of the temperate bacteriophage P2, the immunity repressor, can be detected as a unique band eluting from phosphocellulose columns at 0.12 M-potassium phosphate when differentially labelled with a radioactive amino acid: the band is absent when phages that either have lost gene C through deletion or carry a suppressor-sensitive mutation in the gene are used. The repressor in its monomeric form is about 11,000 in molecular weight. At near physiological salt concentrations, the form predominantly recovered is the dimer. In filter-binding assays, the partially purified repressor binds wild-type P2 DNA strongly. It does not bind DNA of P2 vir94, a deletion that removes all the genetic elements involved in the regulation of lysogeny; it also does not bind, or binds inefficiently, DNA of P2 vir3, a mutation in the operator that controls the early replicative functions of P2. At the concentrations employed, the dimer is the active form in binding. The P2 repressor clearly differs in several features from the well-studied immunity repressor of bacteriophage lambda.