BACTERIOPHAGE-MU MOR PROTEIN REQUIRES SIGMA(70) TO ACTIVATE THE MU-MIDDLE PROMOTER

作者：MATHEE K; HOWE MM

来源：Journal of Bacteriology, 1993, 175(17): 5314-5323.

Transcription during the bacteriophage Mu lytic cycle occurs in three phases: early, middle, and late. Middle transcription requires the early gene product Mor for its activation. Mor protein overproduction was accomplished by fusing the mor gene to an efficient phage T7 promoter and translation initiation region. A protein fraction highly enriched for Escherichia coli RNA polymerase (Esigma70) from the Mor-overproducing strain was able to activate transcription from both the tac promoter (P(tac)) and the Mu middle promoter (P(m)) in vitro. Transcription initiation from P(m) was Mor dependent, and the RNA 5' end was identical to that of in vivo RNA. Addition of anti-sigma70 antibody to transcription reactions containing P(tac) and P(m) resulted in inhibition of transcription from both promoters; addition of purified sigma70 restored transcription. These results indicate that Mor-dependent activation requires sigma70 and therefore imply that Mor is not an alternate sigma factor. This conclusion was further substantiated by a reconstitution experiment with purified proteins in which all three components, Mor, sigma70, and core RNA polymerase, were required for P(m)-dependent transcription in vitro. The sigma70 dependence of Mor-specific transcription and the amino acid sequence similarity between Mor and C (an activator for Mu late transcription) both support the hypothesis that Mor functions mechanistically as an activator protein.

• 出版日期1993-9