FIG. 7.

Model for the signaling pathway that controls σ^G activation. Shown is the proposed sequence of events that originate in the mother cell leading to σ^G activation in the prespore at engulfment. The eight membrane-associated proteins encoded by the spoIIIA locus (SpoIIIAA to SpoIIIAH) and SpoIIIJ participate in conveying the signal that activates σ^G. The spoIIIA-encoded products act from the mother cell across the space delimited by the outer forespore membrane (OFM) and the inner forespore membrane (IFM). SpoIIIJ in turn acts from the prespore. SpoIIIJ may be required for localizing a prespore-specific component (X) of the spoIIIA signaling pathway. The signal conveyed through the spoIIIA-encoded proteins and SpoIIIJ results in the activation of σ^G; it appears to serve in part to antagonize the inhibitory action of SpoIIAB upon σ^G, but it may also involve other, as-yet-unidentified factors. MC, mother cell; FS, engulfed prespore.