A characterization of variant V79 cells selected by tritium uridine suicide

In a previous study, mutagenized cells of the V79 hamster cell line were isolated by tritiated uridine suicide. Preliminary screening from that work indicated that some of the mutants had a decrease in whole cell incorporation of uridine and a decrease in the activity of the enzyme uridine kinase. A rigorous analysis of the uridine kinase was undertaken in this study for three of the variant clones. The results of this study indicate that the mutant cells have a maximal enzyme velocity of only 4% to 6% of that observed for the parental cell line. This decrease in velocity was accompanied by a ten-fold reduction in the Michaelis constant of this enzyme for uridine. These observations are consistent with a mutation in a structural gene for uridine kinase.