SPOIIAB IS AN ANTI-SIGMA FACTOR THAT BINDS TO AND INHIBITS TRANSCRIPTION BY REGULATORY PROTEIN SIGMA-F FROM BACILLUS-SUBTILIS

The sigma(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 Bacillus subtilis. The sigma(F) factor is encoded by the promoter-distal member of sporulation operon spoIIA, which consists of cistrons called spoIIAA, spoIIAB, and spoIIAC. Genetic evidence indicates that the activity of sigma(F) is negatively regulated by the product (SpoIIAB) of the spoIIAB cistron. We now report that SpoIIAB is capable of binding to sigma(F) and inhibiting its capacity to direct transcription by core RNA polymerase from the promoter for a forespore-expressed gene. SpoIIAB is an anti-sigma factor that may be directly involved in the compartmentalization of sigma(F)-directed gene expression.