Cloning and characterization of the immunity region of phage phi 80.

The immunity region of phage phi 80 has been localized. It codes for at least three proteins: a protein of 34 kDa which has the biological properties of the phage repressor, and two other proteins of 9 kDa and 18 kDa which are the first proteins on the rightward operon. These two proteins are negatively regulated by the 34 kDa protein at a divergent promoter site. By position analogy with phage lambda, but not by its biological activity, the 9 kDa protein could be the cro product. The 18 kDa protein is able to block totally UV induction of phage phi 80.