The DNA supercoiling architecture induced by the transcription factor xUBF requires three of its five HMG-boxes.
The formation of a near complete loop of DNA is a striking property of the architectural HMG-box factor xUBF. Here we show that DNA looping only requires a dimer of Nbox13, a C-terminal truncation mutant of xUBF containing just HMG-boxes 1-3. This segment of xUBF corresponds to that minimally required for activation of polymerase I transcription and is sufficient to generate the major characteristics of the footprint given by intact xUBF. Stepwise reduction in the number of HMG-boxes to less than three significantly diminishes DNA bending and provides an estimate of bend angle for each HMG-box. Together the data indicate that a 350 +/- 16 degree loop in 142 +/- 30 bp of DNA can be induced by binding of the six HMG-boxes in an Nbox13 dimer and that DNA looping is probably achieved by six in-phase bends. The positioning of each HMG-box on the DNA does not predominantly involve DNA sequence recognition and is thus an intrinsic property of xUBF.
Stefanovsky
V Y
VY
Departement de Biochimie et Centre de Recherche en Cancérologie de l'Université Laval (CRCUL), Hôtel-Dieu de Québec, Canada.
Bazett-Jones
D P
DP
Pelletier
G
G
Moss
T
T
D001665:Binding Sites; D018983:DNA Footprinting; D004278:DNA, Superhelical / Q000378:metabolism* / Q000648:ultrastructure; D004583:Electrons; D006609:High Mobility Group Proteins; D008958:Models, Molecular; D009154:Mutation; D009690:Nucleic Acid Conformation; D011485:Protein Binding; D017384:Sequence Deletion; D013057:Spectrum Analysis; D013329:Structure-Activity Relationship; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D029867:Xenopus Proteins
D004278:DNA, Superhelical; D006609:High Mobility Group Proteins; D014157:Transcription Factors; C062332:UBFT protein, Xenopus; D029867:Xenopus Proteins