Crystallography Research Today is a free monthly online journal that collates and summarizes the latest research about Crystallography, including details on x-ray crystals, techniques, analyses, structures.

Low resolution structural models of the basic helix-loop-helix leucine zipper domain of upstream stimulatory factor 1 and its complexes with DNA from small angle X-ray scattering data.

Lamber EP, Wilmanns M, Svergun DI

European Molecular Biology Laboratory, Hamburg Outstation, D-22603 Hamburg, Germany.

The upstream stimulatory factor 1 (USF1) belongs to the basic helix-loop-helix leucine zipper (b/HLH/Z) transcription factor family, recognizing the CACGTG DNA motive as a dimer and playing an important role in the regulation of transcription in a variety of cellular and viral promoters. In this study we investigate the USF1 b/HLH/Z domain and its complexes with DNA by small angle x-ray scattering. We present low resolution structural models of monomeric b/HLH/Z USF1 in the absence of DNA and USF1 dimeric (b/HLH/Z)(2)-DNA and tetrameric (b/HLH/Z)(4)-DNA(2) complexes. The data reveal a concentration-dependent USF1 dimer (b/HLH/Z)(2)-DNA-tetramer (b/HLH/Z)(4)-DNA(2) equilibrium. The ability of b/HLH/Z USF1 to form a tetrameric assembly on two distant DNA binding sites as a consequence of increased protein concentration suggest a USF1 concentration-dependant mechanism of transcription activation involving DNA loop formation.

Published 13 December 2007 in Biophys J, 94(1): 193-7.
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