Identification of DNA binding sites for ComE, a key regulator of natural competence in Streptococcus pneumoniae

Natural competence in Streptococcus pneumoniae is regulated by a quorum-sen sing mechanism consisting of a competence-stimulating peptide (CSP), its de dicated secretion apparatus (ComAB), its histidine kinase receptor (ComD) a nd a response regulator (ComE). In this report, we show that ComE is a DNA- binding protein that acts autocatalytically by binding to a region in its o wn promoter. Two additional ComE binding sites were identified in the pneum ococcal genome, one in the promoter region of comAB and the other upstream of an ABC transporter of unknown function. A comparison of the ComE-binding sequences with the sequence motif previously found to be involved in the c o-ordinated expression of the late genes revealed that they are unrelated. These findings indicate that ComE activates transcription of the late genes indirectly, i.e. via one or more intermediate factors.