BRD4 is an extended dimer in solution.A, plot showing intrinsically disordered regions in BRD4 as predicted by PONDR (Predictor of Natural Disordered Regions); VL-XT scores are plotted on the Y axis, and amino acid residue numbers are plotted on the X axis. The arrowheads indicate the locations of functional domains of BRD4. B, size exclusion profile of mouse BRD4 on Superose 6 increase column at 4 °C. Inset shows the standard calibration curve run on same condition. Arrowhead indicates the approximate predicted elution volume of monomeric BRD4. C, 3 to 12% gradient blue native page showing the migration of mouse BRD4. Arrowhead indicates the expected monomeric BRD4 migration. D, 8% SDS-PAGE showing the migration of mouse BRD4. E, sedimentation boundaries of 3 μM mouse BRD4 sedimenting at 50,000 rpm, as observed by absorbance at 280 nm (for clarity symbols show only every third data point of every second scan) and c(s) sedimentation coefficient distribution model (lines). The color temperature from purple to red indicates temporal evolution. F, normalized sedimentation coefficient distributions c(s) distribution plots of mouse BRD4 at different concentrations, 3 μM (purple), 1 μM (blue), and 0.3 μM (cyan) calculated on the basis of absorbance scans at 280 nm as shown in (F).