Methylenetetrahydrofolate-dependent biosynthesis of ribothymidine in transfer RNA of Streptococcus faecalis. Evidence for reduction of the 1-carbon unit by FADH2.
The methyl carbon of ribothymidine in Loop IV of the tRNA of Streptococcus faecalis, Bacillus subtilis, and some other microorganisms is derived directly from 5,10-methylenetetrahydrofolate, not S-adenosylmethionine. The pure enzyme from S. faecalis also requires FADH2. We have obtained evidence that tetrahydrofolate is a product of the reaction and demonstrated that label from [5-3H]5-deazaFMNH2 is incorporated into the methyl moiety of ribothymidine. These data indicate that the enzyme uses methylenetetrahydrofolate solely as a 1-carbon donor and employs FADH2 as a reducing agent in vitro according to the following reaction: tRNA(U psi C) + CH2 = THF + FADH2 leads to tRNA(T psi C) + THF + FAD.
D013293:Enterococcus faecalis / Q000187:drug effects / Q000378:metabolism*; D005182:Flavin-Adenine Dinucleotide / Q000378:metabolism*; D008745:Methylation; D008780:Methyltransferases / Q000378:metabolism; D010084:Oxidation-Reduction; D012343:RNA, Transfer / Q000096:biosynthesis*; D012263:Ribonucleosides / Q000032:analysis; D013045:Species Specificity; D013763:Tetrahydrofolates / Q000494:pharmacology*; D014529:Uridine / Q000031:analogs & derivatives* / Q000096:biosynthesis
D012263:Ribonucleosides; D013763:Tetrahydrofolates; C013123:5,10-methylenetetrahydrofolic acid; D005182:Flavin-Adenine Dinucleotide; C009182:ribothymidine; D012343:RNA, Transfer; D008780:Methyltransferases; C024841:ribothymidyl synthase; D014529:Uridine