Virus-specific capping of tobacco mosaic virus RNA: methylation of GTP prior to formation of covalent complex p126-m7GMP

Abstract In capping cellular mRNAs, a covalent GMP-enzyme intermediate leads to formation of G(5′)ppp(5′)N at the 5′ end of the RNA, which is modified by methylation catalyzed by guanine-7-methyltransferase. Here we show that isolated membranes from tobacco mosaic virus (TMV)-infected plant or insect cells expressing TMV replicase protein p126, synthesized m 7 GTP using S -adenosylmethionine (AdoMet) as the methyl donor, and catalyzed the formation of a covalent guanylate-p126 complex in the presence of AdoMet. The methyl group from AdoMet was incorporated into p126, suggesting that the complex consisted of m 7 GMP-p126. Thus, TMV and alphaviruses, despite their evolutionary distance, share the same virus-specific capping mechanism.