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J Mol Biol. 2006 Jan 27;355(4):798-808. Epub 2005 Nov 22.

Structure of the Escherichia coli FlhDC complex, a prokaryotic heteromeric regulator of transcription.

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Department of Structural Biology, Stanford University School of Medicine, Stanford, CA 94305, USA.


The hetero-oligomeric complex of the FlhD and FlhC proteins (FlhDC) regulates transcription from several flagellar and non-flagellar operons in bacteria. The crystallographic structure of the Escherichia coli FlhDC complex has been solved to 3.0 A resolution, revealing a hexameric FlhD4FlhC2 assembly. In the complex, each FlhC protomer binds an FlhD2 dimer; the conformation of the dimer in the complex differs significantly from its conformation in the absence of FlhC. FlhC has a novel tertiary fold that includes a heretofore unrecognized zinc-binding site in which the ion is ligated by four cysteine residues. Gel shift experiments show that binding of the FlhDC complex to a cognate promoter bends the DNA by approximately 111 degrees . The structure of the FlhDC complex is compatible with models in which a fragment of operator DNA, at least 48 base-pairs in length, wraps around the complex and bends significantly when binding.

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