Salvage of the nucleic acid base queuine from queuine-containing TRNA by animal cells

The incorporation of queuine into tRNA and its fate upon tRNA turnover has been studied in the Vero and L-M cell lines. An assay was developed using ³H]dihydroqueuine to detect the queuine acceptance and, thus, the queuine content of tRNA in intact cells. While L-M cells can use only queuine, Vero cells can use either queuine or its nucleoside, queuosine, to form queunine-containing tRNA. Since queuosine is not a substrate for the enzyme which incorporates queuine into tRNA, Vero cells must generate queuine from its nucleoside. When Vero cells are labelled with ³H]dihydroqueuine, the half life of acid insoluble radioactivity is 52 days in queuine-free medium and 3.1 days in queuine-containing medium, indicating that ³H]dihydroqueuine is salvaged from tRNA and reused by Vero cells, but that exogenous queuine can compete with the salvaged ³H]dihydroqueuine. When L-M cells are labelled with ³H]dihydroqueuine, the half life of the acid insoluble radioactivity is 1.2 days in the presence or absence of queuine, indicating the absence of queuine salvage in L-M cells.