Bacteriophage f1 gene II and X proteins. Isolation and characterization of the products of two overlapping genes.

We have isolated and characterized the 2 major proteins of a dense complex which accumulate in EScherichia coli cells infected with bacteriophage f1 under conditions where the phage gene V protein is inactive (Webster, R. E., and Rementer, M. (1980) J. Mol. Biol. 139, 393-405). The amino acid composition and NH2- and COOH-terminal sequences of the larger polypeptide (estimated molecular weight of 46,000) correspond to those predicted from the DNA sequence for the f1 gene II protein. The other polypeptide (estimated molecular weight of 14,000) has the amino acid composition and COOH-terminal sequence predicted for the f1 X protein, which previously had been found only as a product of an in vitro transcription-translation reaction. The X protein contains N-formylmethionine, cross-reacts with antibodies against gene II protein, and is present in wild type f1-infected bacteria. Thus, X protein is the product of f1 gene X (10), which is contained entirely in, and translated in phase with, gene II.