Further structural and functional analogies between the repressor regions of phages P22 and lambda

Mutants of P22 which have been located in the c2 repressor gene were examined. The most rightward "c2 mutation" was found to define a site that is necessary only for the establishment and not for the maintenance of repressor synthesis. We conclude that this site c27 is an analog of cy mutants in phage lambda which define a promotor for repression establishment (pre). The K5 mutation of P22 maps between c27 and all other c2 mutants. Examination of its biological behavior and direct measurement of repressor activity show that K5 does not affect c2 repression. A model to explain these findings implies that c27 and K5 affect transcripts of opposite directions. P22 c1 mutants do not allow c2 repressor synthesis and we conclude that the activity of c1 product (and presumably c3 product) at the site defined by c27 is necessary for repressor synthesis. The combined activity of c1 and c3 product at c27 is postulated to promote repressor synthesis and block transcription of vegatative phage genes to the right of K5. After repressor synthesis has been established, another site analogous to lambda prm is sufficient for repressor synthesis and c27 is no longer required. These observations and conclusions point to a very close analogy between repressor synthesis and control in phages P22 and lambda.