α factors control clusters of unlinked genes

Sporulation in Bacillus subtilis is regulated by cascades of σ factors. (a) In vegetative cells, σ^A and σ^H are active. On initiation of sporulation, σ^F is active in the forespore and σ^E is active in the mother cell. These σ factors are then superseded by σ^G and σ^K, respectively. The mother cell eventually lyses and releases the mature spore. (b) Factors σ^E and σ^F control the regulons of many genes (ybaN, and so forth, in this illustration). Three examples of the large number of promoters regulated by each σ factor are shown. Each σ factor has a distinct sequence-specific binding preference at the −35 and −10 sequences of target promoters.

[Data from P. Eichenberger et al., J. Mol. Biol. 327, 2003, 945-972; and S. Wang et al., J. Mol. Biol. 358, 2006, 16-37]