Effects of new mutations in the spoIIAB gene of Bacillus subtilis on the regulation of  F and  G activities

Abstract

~~ ~~The spoZZAB gene of BaciZZus subtilis encodes an inhibitor of &, a transcription factor that plays a crucial role in the establishment of prespore-specific gene expression during sporulation. The SpoIIAB protein can probably also inhibit a closely related sigma factor cc, which determines the later phase of prespore-specific transcription. We have isolated two new missense mutations in the spoZZAB gene. spoZZAB28 behaves like the previously described spoZZAB1 mutation, in that it mainly affects the activity of 8. In contrast, the spoZZAB22 mutation seems to be impaired mainly in its ability to inhibit cF. All three missense mutations are clustered in the N-terminal coding region of spoZZAB, suggesting that this region of the protein interacts with the sigma factors. The extreme N-terminal part of SpoIIAB may be specifically concerned with the regulation of cc activity.

Role of the Anti-Sigma Factor SpoIIAB in Regulation of σ G during Bacillus subtilis Sporulation

“…While it seems clear that SpoIIAB can regulate G under nonsporulation conditions or in the predivisional cell at the onset of sporulation, the evidence for a role in the control of G in the prespore is less clear (3,8,19,21,35). On the one hand, SpoIIAB seems to disappear from the prespore coincidently with the first manifestations of G activity, but it persists in the prespore of a spoIIIA mutant (21).…”

“…The pattern of whole-cell decoration could represent cells that have not entered the sporulation pathway and maintain their vegetative state. Because G is autoregulatory (17,47) and because SpoIIAB negatively regulates G in nonsporulating cells (8,35), a mutation impairing SpoIIAB binding could result in increased activity of G . In that case, G activity should have been detected during growth, early in sporulation, and presumably also in the mother cell in strains bearing the spoIIIGE156K allele.…”

“…Activity of G in the mother cell is antagonized by SpoIIAB and LonA. Since G is autoregulatory and SpoIIAB is present in both the prespore and mother cell compartments, we wanted to determine whether SpoIIAB could have a role in the negative regulation of G in the mother cell, as previously suggested (3,8,19,21,35). To investigate this possibility, we fused the coding regions of the wild-type and spoIIIGE156K alleles to the mother cell-specific, E -dependent spoIID promoter (36).…”

“…Expression of spoIIIG prior to the asymmetric division of the sporangial cell blocks sporulation, a phenotype that can be suppressed by a multicopy allele of spoIIAB (21), and certain point mutations in spoIIAB result in expression of G -dependent genes under conditions that do not support efficient sporulation (8,35). Moreover, SpoIIAB binds to G in vitro under conditions that also promote binding of SpoIIAB to F (19), and the structure of a dimer of Bacillus stearothermophilus SpoIIAB in complex with F shows that most of the residues involved in the interaction are conserved in G , but not in other sigma factors (2).…”

“…Two negative regulators of G are known, the anti-sigma factor SpoIIAB and the LonA protease (3,8,19,21,35,40). Expression of spoIIIG prior to the asymmetric division of the sporangial cell blocks sporulation, a phenotype that can be suppressed by a multicopy allele of spoIIAB (21), and certain point mutations in spoIIAB result in expression of G -dependent genes under conditions that do not support efficient sporulation (8,35).…”