Mutually Exclusive Utilization of PR and PRM Promoters in Bacteriophage 434 OR

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American Society for Microbiology

RESUMO

Establishment and maintenance of a lysogen of the lambdoid bacteriophage 434 require that the 434 repressor both activate transcription from the PRM promoter and repress transcription from the divergent PR promoter. Several lines of evidence indicate that the 434 repressor activates initiation of PRM transcription by occupying a binding site adjacent to the PRM promoter and directly contacting RNA polymerase. The overlapping architecture of the PRM and PR promoters suggests that an RNA polymerase bound at PR may repress PRM transcription initiation. Hence, part of the stimulatory effect of the 434 repressor may be relief of interference between RNA polymerase binding to the PRM promoter and to the PR promoter. Consistent with this proposal, we show that the repressor cannot activate PRM transcription if RNA polymerase binds at PR prior to addition of the 434 repressor. However, unlike the findings with the related λ phage, formation of RNA polymerase promoter complexes at PRM and at PR apparently are mutually exclusive. We find that the RNA polymerase-mediated inhibition of repressor-stimulated PRM transcription requires the presence of an open complex at PR. Taken together, these results indicate that establishment of an open complex at PR directly prevents formation of an RNA polymerase-PRM complex.

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