RNA capping by the vaccinia virus guanylyltransferase. Structure of enzyme-guanylate intermediate.

GTP:RNA guanylyltransferase isolated from vaccinia virus catalyzes the transfer of GMP from GTP to the 5' terminus of RNA via an enzyme-guanylate intermediate. Incubation of the purified vaccinia RNA guanylyltransferase with alpha- 32PGTP and MgCl2 yields 32PGMP covalently linked to the Mr = 95,000 subunit. The bond involves the phosphate moiety of GMP and the Ne-amino group of lysine. This was verified by treatment of the isolated 95-kDa subunit-32PGMP complex with sodium periodate, followed by methylamine-catalyzed beta-elimination. The product was then hydrolyzed by alkali producing 32P-labeled lysine (Ne-P)phosphate.