SRPK1 and Clk/Sty protein kinases show distinct substrate specificities for serine/arginine-rich splicing factors

J Biol Chem. 1996 Oct 4;271(40):24569-75. 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.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • 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


  • Nuclear Proteins
  • RNA-Binding Proteins
  • Serine-Arginine Splicing Factors
  • Serine
  • Arginine
  • Clk dual-specificity kinases
  • SRPK1 protein, human
  • Protein-Tyrosine Kinases
  • Protein Serine-Threonine Kinases