DNA synthesis inhibition by ara-G. CEM cells and CEM/ara-G cells were incubated with or without 10 μM ara-G for 3 h, followed by a 4-h incubation with tritiated thymidine. Nuclear (a) and mitochondrial (b) DNA fractions were isolated and subjected to scintillation counting. Percentages are the ratio of the values of thymidine incorporation into the DNA of the cells that had been pre-treated with ara-G relative to those without ara-G pre-incubation. P = 0.0003 for CEM versus CEM/ara-G for nuclear DNA synthesis inhibition by unpaired T test. P = 0.045 for CEM versus CEM/ara-G for mitochondrial DNA synthesis inhibition by unpaired T test. (c) CEM and CEM/ara-G cells were incubated with 10 μM radio-labeled ara-G for 6 h, followed by extraction of nuclear and mitochondrial DNA. Then, the samples were subjected to scintillation counting. The relative ara-G incorporation is the ratio of the value of ara-G incorporation into the DNA of CEM/ara-G cells to that of CEM cells. n.s., not significant. The values shown are the means ± SD of at least three independent experiments.