SRPK1 and Clk/Sty Protein Kinases Show Distinct Substrate Specificities for Serine/Arginine-rich Splicing Factors

摘要: Serine/arginine-rich (SR) proteins are essential for pre-mRNA splicing, and modify the choice of splice site during alternative splicing in a process apparently regulated by protein phosphorylation. Two kinases have been cloned that can phosphorylate SR vitro: SRPK1 Clk/Sty. Here, we show these two same vitro, but has higher specific activity toward ASF/SF2. SRPK1, like Clk/Sty, phosphorylates ASF/SF2 vitro on sites also phosphorylated vivo. Tryptic peptide mapping revealed three phosphopeptides from full-length contain consecutive phosphoserine-arginine residues or phosphoserine-proline residues. In Clk/Sty kinase Ser-Arg, Ser-Lys, Ser-Pro sites, whereas had strong preference Ser-Arg sites. These results suggest may play different roles regulating factors, broader substrate specificity than SRPK1.