Poteete, AR and King, J. (1977) Virology, 76(2), 725-739
Functions of two new genes in Salmonella phage P22 assembly
The capsid of bacteriophage P22 is composed of at least eight protein species, six of which had been identified as the products of known P22 genes. the two smallest proteins, pX of 18,000 daltons, and p-alpha of 15,000 daltons, were not the products of any of the known P22 genes. We have isolated and characterized phage carrying amber mutations in the two genes which code for pX and p-alpha (designated gene 7 and gene 4, respectively). The products of these genes are essential for the formation of viable phage. the gene 7 protein is not needed for particle assembly, but rather for particle infectivity. Restrictive cells infected with a mutant in gene 7 accumulate structures with the sedimentation properities and electron microscopic appearance of wild-type phage. Although the defective 7- particles adsorb to cells, they are unable to recombine with a defective prophage inside the cell or express phage-specific protein synthesis. the 7- phenotype is similar to the phenotypes of amber mutants in genes 16 and 20 [Botstein et al., J. Mol. Biol. 80, 669-695 (1973)]. Genes 7, 16 and 20 map contiguously. The gene 4 product seems to be necessary for the stabiliization of newly DNA-filled phage heads. Restrictive cells infected with a mutant of gene 4 accumulate structures with the sedimentation properties and electron microscopic appearance of the "empty heads" that occur in smaller relative amounts in wild-type lysates. These 4- empty heads are derived from unstably packaged heads inside the cell. the product of gene 4 is not required for cutting phage DNA into mature length piees. The 4- phenotype is similar to the 10- and 26- phenotypes [Lenk et al. Virology 68, 182-199 (1975)]. Genes 4, 10 and 26 map contiguously. All the proteins found in P22 phage and phage precursor particles have been matched with their genes.