title: Stereochemistry of methyl transfer catalyzed by tRNA (m5U54)-methyltransferase--evidence for a single displacement mechanism.
abstract: tRNA (m5U54)-methyltransferase (RUMT) catalyzes the transfer of a methyl group from S-adenosyl-L-methionine (AdoMet) to the 5-carbon of uridine 54 of tRNA. We have determined the steric course of methyl transfer, using (methyl-R)- and (methyl-S)-[methyl-2H1,3H]-AdoMet as the chiral methyl donors, and tRNA lacking the 5-methyl group at position 54 as the acceptor. Following methyl transfer, ribothymidine was isolated and degraded to chiral acetic acid for configurational analysis. Transfer of the chiral methyl group to U54 proceeded with inversion of configuration of the chiral methyl group, suggesting that RUMT catalyzed methyl transfer occurs by a single SN2 displacement mechanism.
authors.affiliation: Department of Pharmaceutical Chemistry and Biochemistry, University of California, San Francisco 94143.
authors.forename: J T
authors.initials: JT
authors.lastname: Kealey
authors.forename: S
authors.initials: S
authors.lastname: Lee
authors.forename: H G
authors.initials: HG
authors.lastname: Floss
authors.forename: D V
authors.initials: DV
authors.lastname: Santi
mesh_terms: D002851:Chromatography, High Pressure Liquid; D004926:Escherichia coli / Q000201:enzymology; D008745:Methylation; D015394:Molecular Structure; D012343:RNA, Transfer / Q000378:metabolism*; D012359:tRNA Methyltransferases / Q000737:chemistry / Q000378:metabolism*
chemical_list: D012343:RNA, Transfer; D012359:tRNA Methyltransferases; C022769:tRNA(uracil-5)-methyltransferase