Virus--Plasmid Interactions: Mutants of Bacteriophage T3 That Abortively Infect Plasmid F-Containing (F+) Strains of Escherichia coli

Bacteriophage T7 and many closely related phages abortively infect plasmid F-containing (F+) strains of Escherichia coli. However phage T3, which is also closely related to T7, grows normally in F+hosts. Mutants of phage T3 that, like T7, are subject to F-mediated restriction have been isolated. These T3 mutants lack or are defective in one or both of two genes that are nonessential for phage growth in F-, wild-type strains. Our results show that the products of phage T3 gene 1.1 or 1.2, or both, are essential for growth and suggest that the comparable phage T7 genes are naturally defective in their ability to counteract the inhibitory effects of F-encoded proteins.