Control of lysogenization by phage P22 I. The P22 cro gene

Abstract

P22 cro − mutants were isolated as one class of phage P22 mutants ( cly mutants) that have a very high frequeney of lysogeny relative to wild-type P22. These mutants: (1) do not form plaques and over-lysogenize relative to wild-type P22 after infection of a wild-type Salmonella host; (2) are defective in anti-immunity; and (3) fail to turn off high-level synthesis of P22 c2-repressor after infection. P22 cro − mutations are recessive and map between the P22 c2 and c1 genes. P22 cro − mutations are suppressed by clear-plaque mutations in the c1 gene, one of which is simultaneously cy −. They are also suppressed, but incompletely, by mutations in the c2 (repressor) gene, especially those that do not completely abolish c2 gene function. Salmonella host mutants have been isolated that are permissive for the lytic growth of the P22 cro − mutants.