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

• Published in: The Journal of biological chemistry 1996-10, Vol.271 (40), p.24569-24575
• Main Authors: Colwill, K, Feng, L L, Yeakley, J M, Gish, G D, Cáceres, J F, Pawson, T, Fu, X D
• Format: Article
• Language: English
• Subjects: Alternative Splicing; Amino Acid Sequence; Arginine - metabolism; Molecular Sequence Data; Mutagenesis; Nuclear Proteins - chemistry; Nuclear Proteins - genetics; Nuclear Proteins - metabolism; Peptide Mapping; Phosphorylation; Protein-Serine-Threonine Kinases - metabolism; Protein-Tyrosine Kinases - metabolism; RNA-Binding Proteins; Serine - metabolism; Serine-Arginine Splicing Factors; Substrate Specificity
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.271.40.24569

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