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Cell fate is determined by cell-specific activation of transcription factor sigma F after asymmetric division during sporulation by Bacillus subtilis. The activity of sigma F is governed by SpoIIAA, SpoIIAB, and SpoIIE, a membrane protein localized at the polar septum. SpoIIAB binds to and inhibits sigma F, and SpoIIAA inhibits SpoIIAB, which prevents SpoIIAB from binding to sigma F. SpoIIAB is also a serine kinase that inactivates SpoIIAA. Here, it is demonstrated that SpoIIE dephosphorylates SpoIIAA-P and overcomes SpoIIAB-mediated inhibition of sigma F. The finding that SpoIIE is a serine phosphatase links asymmetric division to the pathway governing cell-specific gene transcription.

The 0.F factor is a regulatory protein that is responsible for directing gene expression in the forespore compartment of developing cells of the spore-forming soil bacterium BacMlus subtilis. The cJF factor is encoded by the promoter-distal member of sporulation operon spollA, which consists of cistrons called spoIIAA, spollAB, and spollAC. Genetic evidence indicates that the activity of oF is negatively regulated by the product (SpoIIAB) of the spolIAB cistron. We now report that SpoIIAB is capable of binding to cF and inhibiting its capacity to direct transcription by core RNA polymerase from the promoter for a forespore-expressed gene. SpoIIAB is an anti-a factor that may be directly involved in the compartmentalization of arF-directed gene expression.Spore formation in the Gram-positive soil bacterium Bacillus subtilis involves the formation of an asymmetrically positioned septum that partitions the developing cell into two cellular compartments called the forespore and the mother cell (1, 2). Gene expression in the compartments is regulated differentially, with certain genes being expressed in the forespore and others in the mother cell (3, 4). At intermediate to late stages of development, differential gene expression is governed by two compartment-specific RNA polymerase v factors. These are oG, which directs transcription in the forespore, and acK, which directs transcription in the mother cell (5-7). Transcription of the structural genes for crG (spolIIG) and caK (sigK) is, in turn, governed by two earlyacting o factors. These are o7F, which directs the transcription of spoIIIG (8) and other forespore-expressed genes (9), and a'E, which directs the transcription of sigK (10) and other mother-cell-expressed genes (11)(12)(13)(14) 2325The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact.

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