Degradation or Consumption of Exogenous Thymidine in Absence or Presence of Exogenous Deoxycytidine: Effect on DNA Chain Elongation and ( Sup 3 H)Thymidine Incorporation in Control and Uv-Irradiated CHO-K1 Cells

摘要

When CHO-K1 cells monolayers are grown in Ham's F-12 culture medium containing 10% fetal calf serum (medium A) exogenous thymidine (dThd) is degraded to thymine by a putative dThd phosphorylase. Thymine is then poorly incorporated into cellular DNA. When 2 mM deoxycytidine (dCyd) is added to medium A (medium B) no degradation of exogenous dThd occurs; rather dThd is consumed in the synthesis of DNA, presumably via a dThd kinase or other nucleoside salvage pathway. Differences in the kinetics of DNA synthesis, measured by ( sup 3 H)dThd pulse-incorporation or by alkaline sucrose velocity sedimentation, are observed in the two media. In comparison to cells in medium A, DNA chain elongation rates of cells in medium B are faster but total DNA synthesis in these cells, measured by incorporation of ( sup 3 H)dThd, appears to be 2- to 3-fold more sensitive to the inhibitory effects of 10 Jm sup -2 uv-radiation. 23 refs., 3 figs. (ERA citation 13:019596)