Molecular analysis of the packaging signal in bacteriophage CP-T1 of Vibrio cholerae.

We have previously identified a unique site, pac, from which packaging of precursor concatameric viral DNA into proheads starts during the maturation process of bacteriophage CP-T1. The direction of this packaging was determined from restriction enzyme cleavage patterns of CP-T1 DNA. A restriction enzyme generated fragment containing pac was cloned and the surrounding DNA region sequenced. Analysis of the nucleotide sequence revealed numerous repeat regions related to the consensus sequence PuagttGAT.AAT.aa.t. Within the sequenced region an open reading frame encoding a 12260 Mr protein was also identified. This protein appears to share homology with the binding domains of known DNA binding proteins and may represent a putative Pac terminase possessing the specific endonuclease activity required for cleavage at the pac site. Minicell analysis of deletion derivatives of the pac-containing clone revealed a protein of approximately 12,900 Mr encoded within this same region, confirming that this Pac protein is phage encoded.