title: Novel protein kinase of Arabidopsis thaliana (APK1) that phosphorylates tyrosine, serine and threonine.
abstract: During the course of characterizing polymerase chain reaction products corresponding to protein kinases of a higher plant, Arabidopsis thaliana, we found a DNA fragment that potentially codes for a polypeptide with mosaic sequences of two classes of protein kinases, a tyrosine-specific and a serine/threonine-specific one. Overlapping complementary DNA (cDNA) clones coinciding with this fragment were isolated from an A. thaliana cDNA library. From their sequence analyses a protein kinase was predicted composed of 410 amino acid residues (APK1, Arabidopsis protein kinase 1), in which the kinase domain was flanked by short non-kinase domains. Upon expression of APK1 in Escherichia coli cells, several bacterial proteins became reactive with anti-phosphotyrosine antibody but not with the same antibody preincubated with phosphotyrosine, convincing us that APK1 phosphorylated tyrosine residues. APK1 purified from an over-producing E. coli strain showed serine/threonine kinase activity, and no tyrosine kinase activity, towards APK1 itself, casein, enolase, and myosin light chains. APK1 was thus concluded to be a novel type of protein kinase, which could phosphorylate tyrosine, serine, and threonine residues, though tyrosine phosphorylation seemed to occur only on limited substrates. Since the structure of the APK1 N-terminal portion was indicative of N-myristoylation, APK1 might associate with membranes and thereby contribute to signal transduction. The A. thaliana genome contained two APK1 genes close to each other (APK1a and APK1b).
authors.affiliation: Laboratory of Molecular Genetics, Institute for Chemical Research, Kyoto University, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Hirayama
authors.forename: A
authors.initials: A
authors.lastname: Oka
mesh_terms: D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000201:enzymology* / Q000235:genetics; D029681:Arabidopsis Proteins; D001483:Base Sequence; D015139:Blotting, Southern; D003001:Cloning, Molecular; D004247:DNA / Q000302:isolation & purification; D004926:Escherichia coli; D006801:Humans; D015151:Immunoblotting; D008969:Molecular Sequence Data; D010766:Phosphorylation; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases; D011505:Protein-Tyrosine Kinases / Q000235:genetics* / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D012694:Serine / Q000378:metabolism*; D013912:Threonine / Q000378:metabolism*; D014443:Tyrosine / Q000378:metabolism*
chemical_list: D029681:Arabidopsis Proteins; D013912:Threonine; D014443:Tyrosine; D012694:Serine; D004247:DNA; D011494:Protein Kinases; C078571:APK1A protein, Arabidopsis; D011505:Protein-Tyrosine Kinases; D017346:Protein Serine-Threonine Kinases