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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 σ-factors. The expression and activity of all four σ-factors are tightly regulated to ensure the correct sequence of morphological events. Prespore-specific genes are transcribed by two σ-factors, σ F followed by σ G. The gene encoding σ G (sigG) is transcribed by σ F, but also requires the activity of one of the mother-cell-specific σ-factors, σ E, for its expression. The minimal promoter required for dependence on σ 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 σ E-independent promoters resulted in impairment of sporulation. These data support the idea that σ E activity is required for the transcription of sigG.
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