Establishing Lysogenic Transcription in the Temperate Coliphage 186

Abstract

ABSTRACT A single-copy chromosomal reporter system was used to measure the intrinsic strengths and interactions between the three promoters involved in the establishment of lysogeny by coliphage 186. The maintenance lysogenic promoter p L for the immunity repressor gene c I is intrinsically ∼20-fold weaker than the lytic promoter p R . These promoters are arranged face-to-face, and transcription from p L is further weakened some 14-fold by the activity of p R . Efficient establishment of lysogeny requires the p E promoter, which lies upstream of p L and is activated by the phage CII protein to a level comparable to that of p R . Transcription of p E is less sensitive to converging p R transcription and raises c I transcription at least 55-fold. The p E promoter does not occlude p L but inhibits lytic transcription by 50%. This interference is not due to bound CII preventing elongation of the lytic transcript. The p E RNA is antisense to the anti-immune repressor gene apl , but any role of this in the establishment of lysogeny appears to be minimal.