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The transcriptional regulator Spo0A activates transcription from two types of promoters. One type of promoter is used by RNA polymerase containing σA, whereas the other type is used by RNA polymerase containing σH. There are Spo0A-binding sites near the -35 region of both types of promoters. It has been reported that some transcriptional regulators that bind near the -35 regions of promoters directly interact with the sigma subunit of RNA polymerase. Therefore, we looked for evidence that Spo0A interacts with both sigma factors by searching for single amino acid substitutions in these factors that specifically prevent expression from Spo0A-dependent promoters, but that do not decrease activity of Spo0A-independent promoters. Two such amino acid substitutions were isolated in σA and one was isolated in σH. The amino acid substitutions in σA prevented expression from the Spo0A-activated promoters, spollG and spollE, but expression was not impaired from the Spo0A-independent, σA-dependent promoter tms or from the Spo0A-activated, σH-dependent promoter, spollA. The amino acid substitution in σH prevented expression from the spollA promoter but not from the Spo0A-independent promoter, citGp2, which is used by σH-RNA polymerase. All of these amino acid substitutions occur in the carboxyl terminus of the sigma factors. These amino acid substitutions may define the sites of contact between the sigma factors and Spo0A. The ability of response regulators such as Spo0A to interact with multiple sigma factors may increase the variety of responses made by bacteria using a limited number of transcription factors. [ABSTRACT FROM AUTHOR]

Endospore formation in Bacillus subtilis is a morphologically complex process in which the bacterium divides into two compartments (forespore and mother cell) that follow different developmental paths. Compartment-specific transcription in the forespore is initiated by RNA polymerase containing σF, and results in the forespore-speciflc production of σG, which directs most of the subsequent forespore-speciflc transcription. The activity of σF is thought to be restricted to the forespore by the sigma factor antagonist SpollAB. We used antibodies against SpollAB to monitor its accumulation during sporulation. We found that SpollAB accumulates early after the initiation of sporulation, and that it was present in the mother-cell compartment 2h after σF became active in the forespore. SpollAB disappeared preferentially from the forespore during development, and its disappearance from the forespore compartment correlated with the activation of σG in that compartment, raising the possibility that SpollAB may be involved regulating σG activity. We tested whether SpollAB could antagonize σG activity by replacing the σH-dependent promoter that drives expression of spolllG, the structural gene for σG, with a σH-dependent promoter. This resulted in a lytic phenotype that was supressed by the simultaneous expression of a plasmid-borne copy of spollAB. This suggests that SpollAB can suppress this effect of σG Moreover, these cells formed spores efficiently. Since σG the forespore by the σF-dependent transcription of its structural gene that normally occurs in wild-type cells, the forespore-specific activity of σG required for Sporulation appears to have resulted from expression of SpollAB. [ABSTRACT FROM AUTHOR]