Role of RopB in Growth Phase Expression of the SpeB Cysteine Protease ofStreptococcus pyogenes

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Abstract
The Rgg family of transcription regulators is widely distributed among gram-positive bacteria; however, how the members of this family control transcription is poorly understood. In the pathogenStreptococcus pyogenes, the Rgg family member RopB is required for transcription of the gene that encodes the secreted SpeB cysteine protease. Expression of the protease follows distinct kinetics that involves control of transcription in response to the growth phase. In this study, the contribution of RopB to growth phase control was examined. The gene encoding the protease (speB) andropBare transcribed divergently from a 940-bp intergenic region. Primer extension analyses, in conjunction with reporter fusion studies, revealed that the major region controlling the transcription of bothspeBandropBis adjacent toropBand that the promoters for the two genes likely overlap. Furthermore, it was found that RopB is a DNA-binding protein that specifically binds to sequences in this control region. The interrelationship betweenropBandspeBexpression was further reflected in the observation that transcription ofropBitself is subject to growth phase control. However, while expression ofropBfrom a promoter expressed during the early logarithmic phase of growth could complement aropBdeletion mutant, ectopic expression ofropBdid not uncouple the expression ofspeBfrom its growth phase signal. These data implicate other factors in growth phase control and suggest that regulation ofropBexpression itself is not the central mechanism of control.

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