Abstract

The nucleotide sequence of a segment of the bacteriophage P22 chromosome to the left (downstream in the PL operon) of the erf gene was determined. Previous studies (A. C. Fenton and A. R. Poteete, 1984, Virology 134, 148-160) have shown that this region encodes a function that is required for efficient growth of P22 in wild-type, but not in recB- Salmonella. The gene or genes encoding this function were designated abc (anti-recBCD). The DNA sequence reveals three open reading frames that potentially encode polypeptides with molecular weights of 10,900, 11,600, and 6600 (in order of transcription). P22 deletion mutants lacking each of the open reading frames were constructed. In addition, plasmids were constructed placing each of the open reading frames under control of the lac UV5 promoter. The phenotypes of the deletion mutants, and the results of plasmid-phage complementation tests, indicate that Abc activity depends primarily on sequences that encode the 11.6-kDa polypeptide; the 10.9-kDa polypeptide-encoding sequence makes a minor contribution to Abc activity as well. These sequences have been designated abc2 and abc1, respectively. The 6.6-kDa polypeptide is apparently uninvolved.