STUDIES ON 5-FLUOROURACIL-CONTAINING RNA .2. GROSS REDUCTION OF 4-THIOURACIL IN FLUOROURACIL-CONTAINING TRNA FROM ESCHERICHIA COLI

1. 1. Fluorouracil-containing tRNA from Escherichia coli has been shown by ultraviolet absorption measurements and p-hydroxymercuribenzoate titration to be grossly deficient in 4-thiouridine. The extent of deficiency correlates well with the amount of uracil replaced by fluorouracil in the tRNA sample. This supports the idea that uracil, rather than cytosine, acts as the sulfur acceptor in 4-thiouracil formation. 2. 2. The small amount of 4-thiouridine remaining in the fluorouracil-containing tRNA is still capable of undergoing reversible oxidation-reduction. 3. 3. It is proposed that fluorouracil cannot be thiolated as a direct result of the presence of the fluorine atom and not as a result of secondary or tertiary changes in the fluorouracil-containing tRNA. © 1969.