Genetic mapping of rpoD implicates the major sigma factor of Bacillus subtilis RNA polymerase in sporulation initiation.

We have mapped the chromosomal locus of rpoD, which encodes the major sigma factor of Bacillus subtilis RNA polymerase. The rpoD locus lay between aroD and lys, tightly linked to dnaE and inseparable from crsA. Marker order in this region was acf-aroD-dnaE-rpoD(crsA)-spoOG-lys. By transformation using cloned donor DNA from the rpoD region, we identified the gene immediately upstream of rpoD as dnaE, which coded for a 62,000 dalton protein essential for DNA replication. Both dnaE and rpoD were transcribed in the same direction, counterclockwise on the chromosome. The gene functions and organization in the rpoD region are thus similar to those of the E. coli sigma operon. We also used transformation to identify crsA47 as a mutation within the sigma coding region itself. The crsA alteration of sigma renders the sporulation process insensitive to glucose catabolite repression, and also restores sporulation ability to strains carrying early-blocked spoOE, spoOF, and spoOK mutations. Thus the major sigma factor and these spoO gene products directly or indirectly affect the same cellular function.