Nonsense mutants defining seven new genes of the lipid-containing bacteriophage PR4

Thirty-eight new nonsense mutants of the lipid-containing bacteriophage PR4 were isolated. These mutants define seven new viral genes, including the gene encoding the terminal genome protein and an accessory lytic factor. The defective gene products produced in uv-irradiated cells infected with representative mutants from each of the new genetic groups were identified using sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Extracts of uv-irradiated cells infected with nonsense mutants that produce a defective major capsid protein, P2, also lacked two lower molecular weight proteins. The synthesis of all three protein species was recovered in cells infected with one-step revertants of two independent major capsid protein mutants, suggesting the possibility of post-translational processing or overlapping genes. The time course of protein synthesis in wild-type PR4-infected cells was examined using SDS-PAGE. These analyses revealed at least 34 proteins produced following phage PR4 infection that were not present in uninfected control cultures.