Identification of a gene, spoIIR, that links the activation of sigma E to the transcriptional activity of sigma F during sporulation in Bacillus subtilis.

Sporulation of Bacillus subtilis requires the coordinated expression of two separate developmental programs in the mother cell and forespore compartments by sigma E and sigma F, respectively. This coordination is maintained through the action of cross-regulatory factors that control the activities of the various sporulation-specific sigma factors. We present here the isolation and characterization of one such cross-regulatory factor, the spoIIR gene. Using a genetic screen, we have isolated four mutant alleles of spoIIR. These mutants were isolated as expressing sigma F-directed genes but not sigma E-directed genes. The block in sigma E-directed gene expression in spoIIR mutants was caused by an inability to process pro-sigma E to its active form. Cloning and characterization of the spoIIR gene determined that its transcription is directed by sigma F. Thus, SpoIIR is required for linking the activation of sigma E to the activation of sigma F and coordinating the initiation of the two developmental programs required to form a spore.