alpha -Helix E of Spo0A Is Required for capital sigma super(A)- but Not for capital sigma super(H)-Dependent Promoter Activation in Bacillus subtilis

At the onset of endospore formation in Bacillus subtilis, the DNA binding protein Spo0A activates transcription from two types of promoters. The first type includes the spoIIG and spoIIE promoters, which are used by capital sigma super(A)-RNA polymerase, whereas the second type includes the spoIIA promoter, which is used by RNA polymerase containing the secondary sigma factor capital sigma super(H). Previous genetic analyses have identified specific amino acids in alpha -helix E of Spo0A that are important for activation of Spo0A-dependent, capital sigma super(A)-dependent promoters. However, these amino acids are not required for activation of the capital sigma super(H)-dependent spoIIA promoter. We now report the effects of additional single-amino-acid substitutions and the effects of deletions in alpha -helix E. The effects of alanine substitutions revealed one new position (239) in Spo0A that appears to be specifically required for activation of the capital sigma super(A)-dependent promoters. Based on the effects of a deletion mutation, we suggest that alpha -helix E in Spo0A is not directly involved in interaction with capital sigma super(H)-RNA polymerase.