Characteristics of an RNA polymerase population isolated from Bacillus subtilis late in sporulation

The sigma-factor composition of Bacillus subtilis RNA polymerase alters during endospore formation. The best-documented change is the appearance of a major sporulation-specific sigma factor (sigma epsilon), which is an RNA polymerase subunit readily detected at 2 to 4 h into the 8-h sporulation process. To determine the nature of the RNA polymerase in differentiating cells after the period of sigma epsilon abundance, we isolated RNA polymerase from cells that were harvested at 6 h after the onset of sporulation. Highly purified fractions of RNA polymerase from these cells contained at least six proteins which cosedimented with core RNA polymerase (beta beta' alpha 2) during glycerol gradient centrifugation. Most of these proteins were in the size range of 20,000 to 29,000 daltons, although one 90,000-dalton protein was also evident. None of the putative RNA polymerase subunits were present in quantities similar to that observed for sigma epsilon during its period of prominence in the cell but instead resembled the minor vegetative-cell sigma factors in abundance. In vitro transcriptions using cloned B. subtilis DNAs as templates revealed at least two novel transcriptional activities in the enzyme that was isolated from cells at 6 h after the onset of sporulation but absent in an RNA polymerase preparation extracted from cells at 4 h after the onset of sporulation. One of these activities was reconstituted by the addition of a 25,000 to 27,000-dalton protein fraction to core RNA polymerase.