Genetic analysis of the Bacillus subtilis sigG promoter, which controls the sporulation-specific transcription factor sigma G.

At the onset of sporulation in Bacillus subtilis, an asymmetric cell division gives rise to two unequal-sized compartments with distinct developmental fates. The smaller compartment, or prespore, becomes the spore, whilst the larger compartment, or mother cell, eventually lyses after contributing to spore maturation. The fate of each compartment is determined by differential gene expression, controlled by the activation of four compartment-specific sigma-factors. The expression and activity of all four sigma-factors are tightly regulated to ensure the correct sequence of morphological events. Prespore-specific genes are transcribed by two sigma-factors, sigma(F) followed by sigma(G). The gene encoding sigma(G) (sigG) is transcribed by sigma(F), but also requires the activity of one of the mother-cell-specific sigma-factors, sigma(E), for its expression. The minimal promoter required for dependence on sigma(E) was found to stretch to just upstream of the -35 site. Analysis of mutant sigG promoters generated by site-directed mutagenesis and sigG promoters from other species suggests the presence of a binding site for a transcriptional repressor within the sigG promoter region. Replacement of the wild-type promoter with sigma(E)-independent promoters resulted in impairment of sporulation. These data support the idea that sigma(E) activity is required for the transcription of sigG.