Sigma factors are initiation factors that promote the attachment of RNA polymerase to specific initiation sites and are then released. This sigma factor is responsible for the expression of sporulation specific genes in the mother cell. DNA rearrangement occurs at the third hour of sporulation. Selectively expressed in the mother cell chamber of sporulating cells. The spoIVCB gene is an incomplete structural gene that is capable of encoding only the N-terminal half of sigma-K. The remainder of sigma-K is specified by another gene, spoIIIC, that is about 10 kb from spoIVCB on the chromosome. The intervening fragment, called skin, is excised at an intermediate stage of sporulation thus allowing a full coding gene to be produced. Belongs to the sigma-70 factor family.