A) RS domain sequences. B–D) CLK1 and CLK1(ΔN) are incubated with SRSF2 (B), SRSF5 (C), Tra2β1 (C) and 32P-ATP and the reaction is monitored by SDS-PAGE autoradiography. The amount of 32P incorporated in the presence of CLK1 (●) and CLK1(ΔN) (■) are plotted as a function of time. For SRSF2, amplitudes and rate constants of 0.58 μM and 0.050 min−1 for CLK1 and 0.25 μM and 0.095 min−1 for CLK1(ΔN). are obtained For SRSF5, amplitudes and rate constants of 0.45 μM and 0.038 min−1 for CLK1 and 0.19 μM and 0.039 min−1 for CLK1(ΔN) are obtained. For Tra2β1, amplitudes and rate constants of 0.65 μM and 0.081 min−1 for CLK1 and 0.42 μM and 0.030 min−1 for CLK1(ΔN) are obtained.