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Originally published as Biophys J. BioFAST on September 7, 2007.
doi:10.1529/biophysj.107.112243
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Biophysical Journal 94:193-197 (2008)
© 2008 The Biophysical Society

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

Ekaterina P. Lamber * {dagger}, Matthias Wilmanns * and Dmitri I. Svergun * {ddagger}

* European Molecular Biology Laboratory, Hamburg Outstation, D-22603 Hamburg, Germany; {dagger} Harvard Medical School and Brigham and Women's Hospital, Boston, Massachusetts 02115; and {ddagger} Institute of Crystallography, Russian Academy of Sciences, 117333 Moscow, Russia

Correspondence: Address reprint requests to D. Svergun, Tel.: 49-40-89902-125; Fax: 49-40-89902-149; E-mail: svergun{at}embl-hamburg.de.

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-DNA2 complexes. The data reveal a concentration-dependent USF1 dimer (b/HLH/Z)2-DNA-tetramer (b/HLH/Z)4-DNA2 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.






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Copyright © 2008 by the Biophysical Society.