Virulent mutants of bacteriophage phi80.

We have characterized a collection of 11 phi80 mutants that develop in wild-type lysogenic hosts ("virulent" phenotype). All these carry gross DNA rearrangements affecting the right arm of the phi80 chromosome. Our results are consistent with the notion that phi80 development is negatively controlled by the ineA gene product, encoded by one of a cluster of genes (phi80 immunity) located between the phi80 replication and recombination genes. We describe and assign positions for ineA and other genes within the immunity region.