Suppression of defective-sporulation phenotypes by mutations in transcription factor genes of Bacillus subtilis.

Mutations in the Bacillus subtilis major RNA polymerase sigma factor gene (rpoD/crsA47) and a sensory receiver gene (spoOA/rvtA11) are potent intergenic suppressors of several stage 0 sporulation mutations (spoOB, OE, OF & OK). We show here that these suppressors also rescue temperature-sensitive sporulation phenotypes (Spots) caused by mutations in RNA polymerase, ribosomal protein, and protein synthesis elongation factor EF-G genes. The effects of the crsA and rvtA suppressors on RNA polymerase and ribosomal protein spots mutations are similar to those previously described for mutations in another intergenic suppressor gene rev. We have examined the effects of rvtA and crsA mutations on the expression of sporulation-associated membrane proteins, including flagellin and penicillin binding protein 5* (PBP 5*). Both suppressors restored sporulation and synthesis of PBP 5* in several spoO mutants. However, only rvtA restored flagellin synthesis in spoO suppressed backgrounds. The membrane protein phenotypes resulting from the presence of crsA or rvtA suppressors in spoO strains suggests that these suppressors function via distinct molecular mechanisms. The rvtA and crsA mutations are also able to block the ability of ethanol to induce spoO phenocopies at concentrations of ethanol which prevent sporulation in wild type cells. The effects of ethanol on sporulation-associated membrane protein synthesis in wild type and suppressor containing strains have been examined.     

Substitution of RNA-polymerase sigma-subunits and transcription regulation

Recent data on regulation of gene activity in bacteria by substitution of RNA polymerase sigma subunits are reviewed. The htpR gene which controls the switch-on of the Escherichia coli heat-shock protein synthesis codes for sigma 32 subunit. sigma 32-containing RNA polymerase transcribes the heat-shock genes in vitro from specific promoters of no use for RNA polymerase containing the major sigma 70 subunit. Several minor sigma subunits have been found in Bacillus subtilis vegetative cells, in addition to the major sigma 55 subunit, differing in the specificity of promoter recognition. Many B. subtilis genes are controlled by tandemly located promoters recognized by RNA polymerases carrying different sigma subunits. sigma 29 subunit is encoded by spoIIG gene and is probably involved in the regulation of sporulation. Specific sigma subunits for transcribing "middle" or "late" genes are encoded by a number of phages.