Control of gene expression in the temperate coliphage 186. X. The cI repressor directly represses transcription of the late control gene B.

We have found that the repressor of 186 lytic transcription, CI, represses transcription of the late control gene B, with no involvement of the B protein itself. In clone studies we showed that CI repressed transcription from the B promoter and that temperature inactivation of CIts led to B derepression. We conclude that CI repressor directly represses transcription of the B gene and, with prophage induction, it is probable that the inactivation of the CI repressor not only derepresses early lytic transcription, but also derepresses B gene transcription, leading to the activation of transcription from the late promoters.