SPO0A MUTANTS OF BACILLUS-SUBTILIS WITH SIGMA-FACTOR-SPECIFIC DEFECTSIN TRANSCRIPTION ACTIVATION

The transcription factor Spo0A of Bacillus subtilis has the unique abi lity to activate transcription from promoters that require different f orms of RNA polymerase holoenzyme, One class of Spo0A-activated promot er, which includes spoIIEp, is recognized by RNA polymerase associated with the primary sigma factor, sigma A (sigma(A)); the second, which includes spoIIAp, is recognized by RNA polymerase associated with an e arly-sporulation sigma factor, sigma H (sigma(H)). Evidence suggests t hat Spo0A probably interacts directly dth RNA polymerase to activate t ranscription from these promoters. To identify residues of Spo0A that may be involved in transcriptional activation,we used PCR mutagenesis of the entire spo0A gene and designed a screen using two distinguishab le reporter fusions, spoIIE-gus and spoIIA-lacZ. Here we report the id entification and characterization of five mutants of Spo0A that are sp ecifically defective in activation of sigma(A)-dependent promoters whi le maintaining activation of sigma(H)-dependent promoters. These five mutants identify a 14-amino-acid segment of Spo0A, from residue 227 to residue 240, that is required for transcriptional activation of sigma (A)-dependent promoters. This region may define a surface or domain of Spo0A that makes direct contacts with sigma(A)-associated holoenzyme.