The CII protein of bacteriophage 186 establishes lysogeny by activating a promoter upstream of the lysogenic promoter

Abstract

We have shown previously that the cII gene product of the non-lambdoid temperate bacteriophage 186 is required for the establishment of lysogeny. We show here that CII, a potential helix-turn-helix DNA-binding protein, establishes lysogeny by activating a promoter (p E) which spans the apl/cII intergenic region, upstream of the lysogenic promoter, p L. The start site of the p E transcript (+1) has been mapped by primer extension and we have identified the CII binding determinants at p E by DNase I footprinting. CII binds to inverted repeat sequences separated by two turns of the helix, with binding half-sites centred at the −38 and −58 positions of p E. Oligomerisation studies with purified CII protein indicate that a CII tetramer may be the species that binds to this site. We also show that p E is subject to direct negative feedback by the CI repressor.