title: 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.
abstract: 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.
authors.affiliation: European Molecular Biology Laboratory, Hamburg Outstation, D-22603 Hamburg, Germany.
authors.forename: Ekaterina P
authors.initials: EP
authors.lastname: Lamber
authors.forename: Matthias
authors.initials: M
authors.lastname: Wilmanns
authors.forename: Dmitri I
authors.initials: DI
authors.lastname: Svergun
mesh_terms: D001483:Base Sequence; D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors / Q000737:chemistry / Q000648:ultrastructure; D003198:Computer Simulation; D004247:DNA / Q000737:chemistry* / Q000648:ultrastructure*; D008956:Models, Chemical; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D053838:Scattering, Small Angle; D051720:Upstream Stimulatory Factors / Q000737:chemistry* / Q000648:ultrastructure*; D014961:X-Ray Diffraction / Q000379:methods*