title: Characterization of three paralogous members of the Mammalian vaccinia related kinase family.
abstract: Members of the novel vaccinia related kinase (VRK) protein family are characterized by notable sequence homology to the vaccinia virus-encoded B1 kinase (vvB1). vvB1 plays an essential role in viral DNA replication, and Boyle and Traktman have demonstrated that VRK1 enzymes complement the replication defect of a temperature-sensitive viral mutant defective in vvB1 (Boyle, K., and Traktman, P. (2004) J. Virol. 78, 1992-2005). This mammalian kinase family comprises three members, VRK1, VRK2, and VRK3. We have annotated the gene structure for the members of this family and have characterized the enzyme activity and subcellular localization for the human and mouse proteins. VRK1 enzymes show robust autophosphorylation activity and will phosphorylate casein; VRK2 enzymes show modest autophosphorylation activity and will also phosphorylate casein. The VRK3 proteins have key amino acid substitutions that disrupt invariant motifs required for catalytic activity, rendering them enzymatically inert. The VRK1 and VRK2 proteins contain COOH-terminal extracatalytic sequences that mediate intracellular localization. VRK1 proteins possess a basic nuclear localization signal and are indeed nuclear; the extreme C termini of the VRK2 proteins are highly hydrophobic, and the proteins are membrane-associated and colocalize with markers of the endoplasmic reticulum. The NH(2)-terminal region of the VRK3s contains a bipartite nuclear localization signal, which directs these proteins to the nucleus. Our findings provide the basis for further studies of the structure and function of this newly discovered family of protein kinases.
authors.affiliation: Department of Microbiology and Molecular Genetics, Medical College of Wisconsin, Milwaukee, Wisconsin 53226, USA.
authors.forename: R Jeremy
authors.initials: RJ
authors.lastname: Nichols
authors.forename: Paula
authors.initials: P
authors.lastname: Traktman
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002364:Caseins / Q000378:metabolism; D002384:Catalysis; D002460:Cell Line; D002467:Cell Nucleus / Q000201:enzymology; D015870:Gene Expression; D049452:Green Fluorescent Proteins; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D008164:Luminescent Proteins / Q000032:analysis / Q000235:genetics; D051379:Mice; D008969:Molecular Sequence Data; D010766:Phosphorylation; D010802:Phylogeny; D017346:Protein Serine-Threonine Kinases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D011506:Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000032:analysis / Q000235:genetics; D011993:Recombinant Fusion Proteins / Q000032:analysis; D020133:Reverse Transcriptase Polymerase Chain Reaction; D016415:Sequence Alignment; D014162:Transfection
chemical_list: D002364:Caseins; D047908:Intracellular Signaling Peptides and Proteins; D008164:Luminescent Proteins; D011506:Proteins; D012333:RNA, Messenger; D011993:Recombinant Fusion Proteins; C486378:Vrk2 protein, mouse; D049452:Green Fluorescent Proteins; D017346:Protein Serine-Threonine Kinases; C109890:VRK1 protein, human; C109891:VRK2 protein, human; C484518:Vrk1 protein, mouse; C475142:Vrk3 protein, mouse