I investigated the transcriptional regulation of sigmaD synthesis. sigD is part of the fla/che operon, but the gene is also preceded by a promoter of its own. fla/che-dependent transcription is severely reduced in sigD-negative strains. Activity of the promoter in front of sigD is strictly temporally regulated. Deletion of this promoter results in a reduced and delayed activation of transcription of the fla/che operon.