tRNA 4-thiouridine biosynthesis GO:0002937 In E. coli, two genes are involved, nuvA (aka Thi) and NuvC (aka iscS) . NuvA converts the trNA into an unidentified intermediate in an ATP dependent manner. NucC catalyzes the second step, transferring the sulfur from cysteine to an unidentified intermediate. NuvC also participates in thiamine synthesis. hjd biological_process 2012-10-19T15:26:28Z The processes whereby a uridine residue in a tRNA is converted to 4-thiouridine. Typically 4-thiouridine is found at position 8, in many transfer RNAs. tRNA thio-modification