Phosphorylation of nucleosides catalyzed by a mammalian enzyme other than uridine-cytidine kinase

Abstract

Cells of a 3-deazauridine-resistant line of cultured lymphoblastoid cells, RPMI 6410, were found to be essentially devoid of uridine-cytidine kinase activity. The resistant cells tolerated high concentrations of 3-deazauridine in culture, but retained sensitivity, relative to the parent cells, to 6-azauridine and 5-azacytidine, compounds previously recognized as substrates for uridine-cytidine kinase. Intracellular formation of the 5′-monophosphate esters of these analogs is a necessary step in expression of their cytotoxicity. The sensitivity of 3-deazauridine-resistant cells to 6-azauridine and 5-azacytidine is interpreted as indicating that phosphorylation of these analogs by some enzymatic route other than uridine-cytidine kinase may occur in these cells.