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