Expression of spoIIIJ in the Prespore Is Sufficient for Activation of capital sigma super(G) and for Sporulation in Bacillus subtilis

During sporulation in Bacillus subtilis, the prespore-specific developmental program is initiated soon after asymmetric division of the sporangium by the compartment-specific activation of RNA polymerase sigma factor capital sigma super(F). capital sigma super(F) directs transcription of spoIIIG, encoding the late forespore-specific regulator capital sigma super(G). Following synthesis, capital sigma super(G) is initially kept in an inactive form, presumably because it is bound to the SpoIIAB anti-sigma factor. Activation of capital sigma super(G) occurs only after the complete engulfment of the prespore by the mother cell. Mutations in spoIIIJ arrest sporulation soon after conclusion of the engulfment process and prevent activation of capital sigma super(G). Here we show that capital sigma super(G) accumulates but is mostly inactive in a spoIIIJ mutant. We also show that expression of the spoIIIGE155K allele, encoding a form of capital sigma super(G) that is not efficiently bound by SpoIIAB in vitro, restores capital sigma super(G)-directed gene expression to a spoIIIJ mutant. Expression of spoIIIJ occurs during vegetative growth. However, we show that expression of spoIIIJ in the prespore is sufficient for capital sigma super(G) activation and for sporulation. Mutations in the mother cell-specific spoIIIA locus are known to arrest sporulation just after completion of the engulfment process. Previous work has also shown that capital sigma super(G) accumulates in an inactive form in spoIIIA mutants and that the need for spoIIIA expression for capital sigma super(G) activation can be circumvented by the spoIIIGE155K allele. However, in contrast to the case for spoIIIJ, we show that expression of spoIIIA in the prespore does not support efficient sporulation. The results suggest that the activation of capital sigma super(G) at the end of the engulfment process involves the action of spoIIIA from the mother cell and of spoIIIJ from the prespore.