A region in Bacillus subtilis σH required for Spo0A-dependent promoter activity

Spo0A activates transcription in Bacillus subtilis from promoters that are used by two types of RNA polymerase, RNA polymerase containing the primary sigma factor, sigma(A), and RNA polymerase containing a secondary sigma factor, known as sigma(H). The region of sigma(A) near positions 356 to 359 is required for Spo0A-dependent promoter activation, possibly because SpoOA interacts with this region of sigma(A) at these promoters. To determine if the amino acids in the corresponding region of sigma(H) are also important in Spo0A-dependent promoter activation, we examined the effects of single alanine substitutions at 10 positions in sigma(H) (201 to 210). Two alanine substitutions in sigma(H), at glutamine 201 (Q201A) and at arginine 205 (R205A), significantly decreased activity from the Spo0A-dependent, sigma(H)-dependent promoter spoIIA but did not affect expression from the sigma(H)-dependent, Spo0A-independent promoters citGp2 and spoVG. Therefore, promoter activation by SpoOA requires homologous regions in sigma(A) and sigma(H). A mutant form of SpoOA, S231F, that suppresses the sporulation defect caused by several amino acid substitutions in sigma(A) did not suppress the sporulation defects caused by the Q201A and R205A substitutions in sigma(H). This result and others indicate that different surfaces of SpoOA probably interact with sigma(A) and sigma(H) RNA polymerases.