Identification of the repressor and repressor bypass (antirepressor) polypeptides of bacteriophage P1 synthesized in infected minicells.

P1 infected minicells synthesize approximately 50 phage-encoded polypeptides. Phage expression is temporally controlled, demonstrating phage polypeptides synthesized both early and late after infection. The P1 repressor, gpcl1 (Mr = 33,000), repressor bypass polypeptide, gpreb A (Mr = 27,500) and cistron 10 product, (gp10) (Mr = 64,000), have been identified by infection of minicells with P1 amber mutants. The beta-lactamase gene product (gpbla) carried by the closely related P7 and the chloramphenicol acetyl-transferase gene product (gpcat) carried by P1 Cm (in Tn9) have been demonstrated. Infection of minicells by P1virs or P1c4 mutants results in increased synthesis of gpreb A and a second polypeptide designated gpreb B (Mr = 40,000). The P1vir11 mutation leads to increased synthesis of a small polypeptide (Mr = 3,500) but does not affect the amount of gpc1 synthesized.