METHYLTRANSFERASE ACTIVITY OF THE INSECT ORBIVIRUS JKT-7400 - PHOTOAFFINITY-LABELING OF A MINOR VIRION PROTEIN, VP4, WITH S-ADENOSYLMETHIONINE

JKT-7400 virus is an orbivirus originally isolated from Culex mosquito es. In earlier work we had described the viral structural proteins and presented evidence suggesting that a minor protein, VP6, located in t he viral core was the Viral guanylyltransferase. We now show that grad ient-purified JKT-7400 virions possess a methyltransferase (MTase) act ivity which can use GTP or GDP as the methyl acceptor. The apparent K- m of the MTase for S-adenosylmethionine (AdoMet) was 25 mu M. Photoaff inity labeling experiments in which H-3-[methyl]-AdoMet was incubated with Virions or viral cores demonstrated labeling of VP4, a minor prot ein present in the Viral core, suggesting that this protein is the vir al MTase. Labeling of VP4 was inhibited by addition of unlabeled AdoMe t or S-adenosylhomocysteine (AdoHcy). (C) 1997 Academic Press.