Polarity withinpMandpEpromoted phage lambdacI-rexA-rexBtranscription and its suppression

Abstract

The cI-rexA-rexB operon of bacteriophage λ confers 2 phenotypes, Imm and Rex, to lysogenic cells. Immunity to homoimmune infecting λ phage depends upon the CI repressor. Rex exclusion of T4rII mutants requires RexA and RexB proteins. Both Imm and Rex share temperature-sensitive conditional phenotypes when expressed from cI[Ts]857 but not from cI+λ prophage. Plasmids were made in which cI-rexA-rexB was transcribed from a non-lambda promoter, pTet. The cI857-rexA-rexB plasmid exhibited Ts conditional Rex and CI phenotypes; the cI+-rexA-rexB plasmid did not. Polarity was observed within cI-rexA-rexB transcription at sites in cI and rexA when CI was nonfunctional. Renaturation of the Ts CI857 repressor, allowing it to regain functionality, suppressed the polar effect on downstream transcription from the site in cI. The second strong polar effect near the distal end of rexA was observed for transcription initiated from pE. The introduction of a rho Ts mutation into the host genome suppressed both polar effects, as measured by its suppression of the conditional Rex phenotype. Strong suppression of the conditional Rex[Ts] phenotype was imparted by ssrA and clpP (polar for clpX) null mutations, suggesting that RexA or RexB proteins made under conditions of polarity are subject to 10Sa RNA tagging and ClpXP degradation.Key words: bacteriophage lambda (λ), Rex exclusion, CI and Cro repressors, Rho, ClpXP, 10Sa RNA tagging.