Methyltransferase Activity of the Insect Orbivirus JKT-7400: Photoaffinity Labeling of a Minor Virion Protein, VP4, withS-Adenosylmethionine

Abstract

JKT-7400 virus is an orbivirus originally isolated fromCulexmosquitoes. In earlier work we had described the viral structural proteins and presented evidence suggesting that a minor protein, VP6, located in the viral core was the viral guanylyltransferase. We now show that gradient-purified JKT-7400 virions possess a methyltransferase (MTase) activity which can use GTP or GDP as the methyl acceptor. The apparentKmof the MTase forS-adenosylmethionine (AdoMet) was 25 μM.Photoaffinity labeling experiments in which3H-[methyl]-AdoMet was incubated with virions or viral cores demonstrated labeling of VP4, a minor protein present in the viral core, suggesting that this protein is the viral MTase. Labeling of VP4 was inhibited by addition of unlabeled AdoMet orS-adenosylhomocysteine (AdoHcy).