Prokaryotic transcription regulators: more than just the helix-turn-helix motif.

Over the past two years, the structures of many prokaryotic transcriptional regulators have been solved, and several of them have revealed the structural mechanism of gene regulation. The crystal structure of BmrR-TPP-DNA reveals a novel mechanism of transcription activation, whereby the drug-bound protein activates the bmr promoter by local DNA unwinding and base pair disruption. Myristoyl-CoA induces FadR by a three-helix pushing mechanism, whereas TetR employs a helical pendulum motion to regulate expression. The structures of AbrB, and DNA complexes of Rob and MuR unveil a novel DNA-binding motif, 'the looped-hinge helix', and new uses of the helix-turn-helix and winged helix motifs in DNA binding.