title: The human cytomegalovirus UL44 protein is a substrate for the UL97 protein kinase.
abstract: The human cytomegalovirus UL97 protein is an unusual protein kinase that is able to autophosphorylate and to phosphorylate certain exogenous substrates, including nucleoside analogs such as ganciclovir. However, no natural substrate of UL97 in infected cells has been identified. We report here that recombinant UL44 protein became radiolabeled when incubated with recombinant UL97 and [(32)P]ATP and that both proteins could be coimmunoprecipitated by an antibody that recognizes either protein. Subsequent studies showed that highly purified, recombinant UL97 phosphorylated purified, recombinant UL44. This phosphorylation occurred on serine and threonine residues and was sensitive to inhibition by maribavir and to a mutation that inactivates UL97 catalytic activity. Two-dimensional gel electrophoresis revealed the absence of specific phosphorylated forms of UL44 in immunoprecipitates from lysates of cells infected with a UL97 null mutant virus or with wild-type virus in the presence of maribavir. The results indicate that UL97 is sufficient to phosphorylate UL44 in vitro and is necessary for the normal phosphorylation of UL44 in infected cells. This strongly suggests that UL44 is a natural substrate of UL97.
authors.affiliation: Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, 250 Longwood Avenue, Boston, MA 02115, USA.
authors.forename: Paula M
authors.initials: PM
authors.lastname: Krosky
authors.forename: Moon-Chang
authors.initials: MC
authors.lastname: Baek
authors.forename: Wan Jin
authors.initials: WJ
authors.lastname: Jahng
authors.forename: Imma
authors.initials: I
authors.lastname: Barrera
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Harvey
authors.forename: Karen K
authors.initials: KK
authors.lastname: Biron
authors.forename: Donald M
authors.initials: DM
authors.lastname: Coen
authors.forename: Phiroze B
authors.initials: PB
authors.lastname: Sethna
mesh_terms: D000818:Animals; D016367:Baculoviridae / Q000235:genetics; D002478:Cells, Cultured; D003587:Cytomegalovirus / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D010766:Phosphorylation; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000235:genetics / Q000378:metabolism*; D011233:Precipitin Tests; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D018411:Spodoptera; D013379:Substrate Specificity; D014764:Viral Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D004268:DNA-Binding Proteins; C072217:ICP36 protein, Cytomegalovirus; D011993:Recombinant Fusion Proteins; D014764:Viral Proteins; D017853:Phosphotransferases (Alcohol Group Acceptor); C075365:ganciclovir kinase