title: A distinct cyclin-dependent kinase-activating kinase of Arabidopsis thaliana.
abstract: The activation of cyclin-dependent kinases (CDKs) requires phosphorylation of a threonine residue within the T-loop catalyzed by CDK-activating kinases (CAKs). Thus far no functional CAK homologue has been reported in plants. We screened an Arabidopsis cDNA expression library for complementation of a budding yeast CAK mutant. A cDNA, cak1At, was isolated that suppressed the CAK mutation in budding yeast, and it also complemented a fission yeast CAK mutant. cak1At encodes a protein related to animal CAKs. The CAK similarity was restricted to the conserved kinase domains, leading to classification of Cak1At as a distinct CDK in the phylogenetic tree. Immunoprecipitates with the anti-Cak1At antibody phosphorylated human CDK2 at the threonine residue (T160) within the T-loop and activated its activity to phosphorylate histone H1. Whereas CAKs in animals and fission yeast are involved in regulation of the cell cycle and basal transcription by phosphorylating the carboxyl-terminal domain (CTD) of the largest subunit of RNA polymerase II, Cak1At did not phosphorylate the CTD. An Arabidopsis CTD-kinase isolated separately from Cak1At was shown to interact with the yeast protein p13(suc1), but it had no CDK2-kinase activity. Therefore, the CTD of RNA polymerase II is probably phosphorylated by a Cdc2-related kinase distinct from Cak1At. cak1At is a single-copy gene in Arabidopsis and is highly expressed in proliferating cells of suspension cultures.
authors.affiliation: Institute of Molecular and Cellular Biosciences, University of Tokyo, Yayoi 1-1-1, Bunkyo-ku, Tokyo 113-0032, Japan. mumeda@imcbns.iam.u-tokyo.ac.jp
authors.forename: M
authors.initials: M
authors.lastname: Umeda
authors.forename: R P
authors.initials: RP
authors.lastname: Bhalerao
authors.forename: J
authors.initials: J
authors.lastname: Schell
authors.forename: H
authors.initials: H
authors.lastname: Uchimiya
authors.forename: C
authors.initials: C
authors.lastname: Koncz
mesh_terms: D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000201:enzymology*; D029681:Arabidopsis Proteins; D042846:CDC2-CDC28 Kinases; D002455:Cell Division; D003001:Cloning, Molecular; D051357:Cyclin-Dependent Kinase 2; D018844:Cyclin-Dependent Kinases / Q000378:metabolism; D018076:DNA, Complementary / Q000235:genetics; D004789:Enzyme Activation; D015870:Gene Expression; D017343:Genes, Plant; D005816:Genetic Complementation Test; D006801:Humans; D008969:Molecular Sequence Data; D010766:Phosphorylation; D010802:Phylogeny; D017346:Protein Serine-Threonine Kinases / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D000095043:Cyclin-Dependent Kinase-Activating Kinase
chemical_list: D029681:Arabidopsis Proteins; D018076:DNA, Complementary; C112244:Cak1at protein, Arabidopsis; D017346:Protein Serine-Threonine Kinases; D042846:CDC2-CDC28 Kinases; C495894:CDK2 protein, human; D051357:Cyclin-Dependent Kinase 2; D018844:Cyclin-Dependent Kinases; D000095043:Cyclin-Dependent Kinase-Activating Kinase