Transcription factors ERα and Sox2 have differing multiphasic DNA- and RNA-binding mechanisms

(A) ERα_DBD-Ext- and (B) Sox2_HMG-ligand-binding affinities. Equilibrium (end point) anisotropy values are plotted as function of protein concentration. Equilibrium data were fit to the Hill binding equation (Equation 1) or two-transition binding equation (Equation 2) via regression on linear axes to determine the apparent equilibrium dissociation constants () and Hill coefficients (n). Values for are in units of nanomolarity (nM). Dots are data points, and solid lines are regression fits. Data are from a single experiment for each ligand, and binding constant values are the average of independent experiments (one to three per interaction; see Table 1 for error analysis). We note that the ΔERE is approximately half the ligand concentration for the assay, suggesting that the true K_d may be even lower, and that the apparent Hill coefficient (n) may be slightly inflated by the anomalous tight-binding curve. Thus, we make no assertion of positive cooperativity for the ERα_DBD-Ex–ΔERE interaction. (*) Two-transition binding curves with values shown alongside the proportion of the binding signal dynamic range attributable to the lower ; no applicable Hill coefficient values.