NovelspoIIEMutation That Causes Uncompartmentalized σFActivation inBacillus subtilis

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Abstract
During sporulation,Bacillus subtilisundergoes an asymmetric division that results in two cells with different fates, the larger mother cell and the smaller forespore. The protein phosphatase SpoIIE, which is required for activation of the forespore-specific transcription factor σF, is also required for optimal efficiency and timing of asymmetric division. We performed a genetic screen forspoIIEmutants that were impaired in sporulation but not σFactivity and isolated a strain with the mutationspoIIEV697A. The mutant exhibited a 10- to 40-fold reduction in sporulation and a sixfold reduction in asymmetric division compared to the parent. Transcription of the σF-dependentspoIIQpromoter was increased more than 10-fold and was no longer confined to the forespore. The excessive σFactivity persisted even when asymmetric division was prevented. Disruption ofspoIIGBdid not restore asymmetric division to thespoIIEV697Amutant, indicating that the deficiency is not a consequence of predivisional activation of the mother cell-specific transcription factor σE. Deletion of the gene encoding σF(spoIIAC)restored asymmetric division; however, a mutation that dramatically reduced the number of promoters responsive to σF,spoIIAC561(spoIIACV233 M), failed to do so. This result suggests that the block is due to expression of one of the small subset of σF-dependent genes expressed in this background or to unregulated interaction of σF with some other factor. Our results indicate that regulation of SpoIIE plays a critical role in coupling asymmetric division to σFactivation in order to ensure proper spatial and temporal expression of forespore-specific genes.