Forespore-specific transcription of a gene in the signal transduction pathway that governs Pro-sigma K processing in Bacillus subtilis.

We present studies on the regulation of a developmental gene (spoIVB) whose product is required at a late stage of morphogenesis during the process of sporulation in Bacillus subtilis. Earlier work implicated the spoIVB gene product in a signal-transduction pathway that governs the conversion of pro-sigma K to the mature and active form of the mother cell sigma factor, sigma K, in response to a signal generated within the forespore chamber of the sporangium. We now show that (1) spoIVB is induced at the engulfment stage of sporulation, (2) this transcription is restricted to the forespore, and (3) spoIVB is under the direct control of the forespore sigma factor sigma G. The discovery that spoIVB is a forespore-expressed gene suggests that the spoIVB gene product, or a developmental event under its control, triggers the processing of pro-sigma K and thereby mediates the coupling of sigma K-directed gene expression in the mother cell to sigma G-directed gene expression in the forespore. We also show that spoIVB transcription is partially dependent on the action of the mother cell regulatory gene spoIIID, a finding that suggests that the transcription of certain forespore-expressed genes is influenced by events in the mother cell.