Cell-cell and starvation signals are funneled through the phosphorelay
to initiate sporulation by activating the transcription regulator Spo
OA. Activation of SpoOA leads to synthesis of the transcription factor
s sigma(F) and sigma(E). Substantial advances have been made in our un
derstanding of the signal circuitry of the phosphorelay and of the cel
l-type-specific activation of the sigma factors.