title: N-terminus of the protein kinase CLK1 induces SR protein hyperphosphorylation.
abstract: SR proteins are essential splicing factors that are regulated through multisite phosphorylation of their RS (arginine/serine-rich) domains by two major families of protein kinases. The SRPKs (SR-specific protein kinases) efficiently phosphorylate the arginine/serine dipeptides in the RS domain using a conserved docking groove in the kinase domain. In contrast, CLKs (Cdc2-like kinases) lack a docking groove and phosphorylate both arginine/serine and serine-proline dipeptides, modifications that generate a hyperphosphorylated state important for unique SR protein-dependent splicing activities. All CLKs contain long flexible N-terminal extensions (140-300 residues) that resemble the RS domains present in their substrate SR proteins. We showed that the N-terminus in CLK1 contacts both the kinase domain and the RS domain of the SR protein SRSF1 (SR protein splicing factor 1). This interaction not only is essential for facilitating hyperphosphorylation, but also induces co-operative binding of SRSF1 to RNA. The N-terminus of CLK1 enhances the total phosphoryl contents of a panel of physiological substrates including SRSF1, SRSF2, SRSF5 and Tra2β1 (transformer 2β1) by 2-3-fold. These findings suggest that CLK1-dependent hyperphosphorylation is the result of a general mechanism in which the N-terminus acts as a bridge connecting the kinase domain and the RS domain of the SR protein.
authors.affiliation: *Department of Pharmacology, University of California, San Diego, La Jolla, CA 92093-0636, U.S.A.
authors.forename: Brandon E
authors.initials: BE
authors.lastname: Aubol
authors.affiliation: *Department of Pharmacology, University of California, San Diego, La Jolla, CA 92093-0636, U.S.A.
authors.forename: Ryan M
authors.initials: RM
authors.lastname: Plocinik
authors.affiliation: *Department of Pharmacology, University of California, San Diego, La Jolla, CA 92093-0636, U.S.A.
authors.forename: Malik M
authors.initials: MM
authors.lastname: Keshwani
authors.affiliation: *Department of Pharmacology, University of California, San Diego, La Jolla, CA 92093-0636, U.S.A.
authors.forename: Maria L
authors.initials: ML
authors.lastname: McGlone
authors.affiliation: *Department of Pharmacology, University of California, San Diego, La Jolla, CA 92093-0636, U.S.A.
authors.forename: Jonathan C
authors.initials: JC
authors.lastname: Hagopian
authors.affiliation: †Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, CA 92093-0636, U.S.A.
authors.forename: Gourisankar
authors.initials: G
authors.lastname: Ghosh
authors.affiliation: ‡Department of Cellular and Molecular Medicine, University of California, San Diego, La Jolla, CA 92093-0636, U.S.A.
authors.forename: Xiang-Dong
authors.initials: XD
authors.lastname: Fu
authors.affiliation: *Department of Pharmacology, University of California, San Diego, La Jolla, CA 92093-0636, U.S.A.
authors.forename: Joseph A
authors.initials: JA
authors.lastname: Adams
mesh_terms: D000818:Animals; D001120:Arginine / Q000378:metabolism; D006801:Humans; D051379:Mice; D009687:Nuclear Proteins / Q000378:metabolism*; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D012326:RNA Splicing; D016601:RNA-Binding Proteins / Q000378:metabolism*; D012694:Serine / Q000378:metabolism; D000068103:Serine-Arginine Splicing Factors; D013379:Substrate Specificity
chemical_list: D009687:Nuclear Proteins; D016601:RNA-Binding Proteins; D000068103:Serine-Arginine Splicing Factors; D012694:Serine; D001120:Arginine; C066780:Clk dual-specificity kinases; D011505:Protein-Tyrosine Kinases; D017346:Protein Serine-Threonine Kinases