Effects of the ID regions (residues 182 to 247 and 366 to 422) on the RNA binding activity of the CTD. (A through C) Fitting of the binding isotherms of NP248-365 (CTD) (A), NP248-422 (B), and NP182-365 (C), based on the EMSA results. Each binding isotherm represents the overall fitting against three independent experiments, taking into account the standard deviation of each data point. (D through F) Representative EMSA results for NP248-365 (D), NP248-422 (E), and NP182-365 (F).