MULTILEVEL REGULATION OF THE SPORULATION TRANSCRIPTION FACTOR SIGMA(K) IN BACILLUS-SUBTILIS

Gene expression in the mother-cell compartment of the Bacillus subtilis sporangium is governed in part by the sporulation transcription factor sigma(K). The production of sigma(K) is controlled at three levels: by a chromosomal rearrangement that generates the sigma(K)-coding sequence (sigK), by compartment-specific transcription of sigK, and by conversion of the inactive pro-protein product of sigK (pro-sigma(K)) to sigma(K). To investigate the function of these multiple levels of regulation, we constructed a set of strains that bypass the chromosomal rearrangement, pro-protein processing, or both levels of control. Here we show that one of the functions of the chromosomal rearrangement and pro-protein processing is to prevent inappropriate production of sigma(K) under nonsporulation conditions. In the absence of both of these levels of control, a low level of sigma(K)-directed gene expression is observed during stationary phase after growth in rich medium. The appearance of sigma(K) under these conditions is probably due to a low level of sigma(K)-directed transcription from the sigK promoter in a positive feedback loop. We also report the construction of a strain that produces high levels of sigma(K) during growth. Using this strain, we demonstrate that the production of sigma(K) during growth is sufficient to induce a cascade of gene expression that closely mimics late events in the mother-cell line of gene expression.