Control of the Expression and Compartmentalization of σ G Activity during Sporulation of Bacillus subtilis by Regulators of σ F and σ E

During formation of spores byBacillus subtilis the RNA polymerase factor σG ordinarily becomes active during spore formation exclusively in the prespore upon completion of engulfment of the prespore by the mother cell. Formation and activation of σG ordinarily requires prior activity of σF in the prespore and σE in the mother cell. Here we report that inspoIIA mutants lacking both σF and the anti-sigma factor SpoIIAB and in which σE is not active, σG nevertheless becomes active. Further, its activity is largely confined to the mother cell. Thus, there is a switch in the location of σG activity from prespore to mother cell. Factors contributing to the mother cell location are inferred to be read-through ofspoIIIG , the structural gene for σG , from the upstreamspoIIG locus and the absence of SpoIIAB, which can act in the mother cell as an anti-sigma factor to σG . When thespoIIIG locus was moved away fromspoIIG to the distalamyE locus, σG became active earlier in sporulation inspoIIA deletion mutants, and the sporulation septum was not formed, suggesting that premature σG activation can block septum formation. We report a previously unrecognized control in which SpoIIGA can prevent the appearance of σG activity, and pro-σE (but not σE ) can counteract this effect of SpoIIGA. We find that in strains lacking σF and SpoIIAB and engineered to produce active σE in the mother cell without the need for SpoIIGA, σG also becomes active in the mother cell.