Sigma factors are initiation factors that promote the attachment of RNA polymerase to specific initiation sites and are then released. This sigma factor directs the transcription of crystal protein genes, a sporulation-regulated event. Is probably activated at the time of septum formation separating the mother cell from the nascent endospore, (stage II). Proteolytically cleaved in the N-terminus probably by a SpoIIGA homolog to yield the active peptide. Belongs to the sigma-70 factor family.