SUMMARYGene expression in members of the familyBacillaceaebecomes compartmentalized after the distinctive, asymmetrically located sporulation division. It involves complete compartmentalization of the activities of sporulation-specific sigma factors, σFin the prespore and then σEin the mother cell, and then later, following engulfment, σGin the prespore and then σKin the mother cell. The coupling of the activation of σFto septation and σGto engulfment is clear; the mechanisms are not. The σ factors provide the bare framework of compartment-specific gene expression. Within each σ regulon are several temporal classes of genes, and for key regulators, timing is critical. There are also complex intercompartmental regulatory signals. The determinants for σFregulation are assembled before septation, but activation follows septation. Reversal of the anti-σFactivity of SpoIIAB is critical. Only the origin-proximal 30% of a chromosome is present in the prespore when first formed; it takes ≈15 min for the rest to be transferred. This transient genetic asymmetry is important for prespore-specific σFactivation. Activation of σErequires σFactivity and occurs by cleavage of a prosequence. It must occur rapidly to prevent the formation of a second septum. σGis formed only in the prespore. SpoIIAB can blockσGactivity, but SpoIIAB control does not explain why σGis activated only after engulfment. There is mother cell-specific excision of an insertion element insigKand σE-directed transcription ofsigK, which encodes pro-σK. Activation requires removal of the prosequence following aσG-directed signal from the prespore.