The biology of enhancer-dependent transcriptional regulation in bacteria: insights from genome sequences.

The bacterial transcription factor sigma(N) (sigma-N, sigma-54, RpoN) confers upon RNA polymerase (RNAP) properties distinct from those of the major house-keeping form of RNAP, which contains sigma(70) (sigma-70, RpoD). Transcription by RNAP containing sigma(N) is subject to enhancer-dependent regulation. Far from being an 'oddity' or 'exception to the rule', the occurrence of sigma(N) in the genome sequences of such diverse bacteria as Aquifex aeolicus, Bacillus subtilis, Chlamydia spp. and Borrelia burgdorferi argues for its biological importance. The availability of complete genome sequences of several (eu)bacteria offers an opportunity to extend our understanding of this special form of transcriptional regulation. By scanning their genome sequences, new functions have been predicted for enhancer-dependent transcription in A. aeolicus, Chlamydia trachomatis, Escherichia coli, Treponema pallidum and B. burgdorferi.