Has a role in pre-mRNA splicing. Phosphorylates SF2/ASF. ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Identified in the spliceosome C complex. Interacts with Clk1 C-terminus. Ubiquitous. Phosphorylated by Clk1. Belongs to the protein kinase superfamily. CMGC Ser/Thr protein kinase family. Extended N-terminus.