The replication of bacteriophage f1: gene V protein regulates the synthesis of gene II protein.

Two filamentous phage gene products are required for the replication of phage DNA. One of these, the gene II protein, is a site-specific endonuclease required for all phage-specific DNA synthesis. The other, the gene V protein, is a single-stranded DNA-binding protein required only for single-strand synthesis. Purified gene V protein, when added to an in vitro protein synthesizing system programmed by f1 DNA, specifically inhibits the synthesis of gene II protein. Inhibition seems to be translational, since synthesis of gene II protein from an RNA template is also inhibited by gene V protein. Gene V protein control of gene II expression can account for the regulation of the level of expression of the filamentous phage genome.