Sporulation in the gram-positive bacterium, Bacillus subtilis, is initiated by nutrient stress and terminates in the appearance of a dormant, resistant endospore. this process is mainly controlled at the level of transcription. Several RNA polymerases with different promoter specificities read subsets of genes, in a temporally ordered sequence, so that new gene products, reflecting the differential state, are produced. These promoter specificities are determined by alternative O factors which associate signal and the signal transduction mechanism which activates this cascade of successive waves of transcriptional specificity. Our laboratory has cloned and characterized the spoOH gene, one of the 7 early spoO genes which are essential for the environmentally determined transition from vegetative growth to the first apparent stage in sporulation, the formation of the asymmetric spore septum. We have shown that the spoOH gene product is oH, which as part of a holoenzyme, EsigmaH, transcribes several genes that are selectively expressed at the beginning of the sporulation process. The spoOH gene is also expressed during vegetative growth, and requires a functional spoOA gene. The spoOA protein, on the basis of its amino acid sequence similarity to other bacterial effector proteins and its unique role in the control of all late growth phenomena, seems to be part of the signal transduction machinery. We will study the role of the spoOA protein and other regulatory molecules in spoOH expression and characterize cis sequences in the spoOH promoter region which interact with these effectors. There seems to be a contradiction in the fact that spoOH is expressed during growth, but the genes dependent on EsigmaH are and functional EsigmaH during growth, to see whether these levels explain the temporal which control EsigmaH activity, in vivo. Since holoenzyme assembly from core and sigma factors could be a step at which RNA polymerase activity is regulated, in general, we will study the nature of core polymerase/alternative sigma factor interaction. Since the sporulation process is dispensible for B. subtilis survival, we can isolate mutations in core protein genes which cause a sporulation defective phenotype as a result of core polymerase inability to associate with sigmaH. Second site suppressors mapping in the spoOH gene will also be isolated. The sequencing of genes with these mutations should reveal protein domains essential for core/sigmaH interaction.
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