PHOSPHORYLATION OF TRITIATED THYMIDINE BY L929 MOUSE FIBROBLASTS

Evidence is presented that only cells in S-phase and early G2 phosphorylate exogenously supplied thymidine. It is believed that this is due, in part, to increased levels of thymidine kinase during S-phase, but primarily to a feedback mechanism whereby the TTP which accumulates in early G2 inhibits thymidine kinase. A second effect of increased levels of thymidylate is to repress synthesis of thymidine kinase and this accentuates the effet of the feedback inhibition. The intranuclear localisation of thymidylate is attributed to the localisation of thymidine kinase in the nucleus. © 1969.