It has become increasingly apparent that t,hymidine kinase (ATP: thymidine 5’-phosphotransferase, EC 2.7.1.21) is a site of specific regulatory control of the levels of uracil and thymine deoxyribonucleotides within cells (1, 2). The synthesis of thymidine kinase is subject to control by repression (3, 4) and the activity of the enzyme can be strikingly inhibited by thymidine triphosphate (end ...

When [3H]thymidine is added to HeLa cells grown in thymidine-free medium it is incorporated into DNA almost immediately at full specific activity, blocking any further incorporation of de novo synthesized thymidine nucleotides. Apparently, de novo nucleotide pools [Baumunk, C.N. & Friedman, D.L. (1971) Cancer Res. 31, 1930--35] and salvage nucleotide pools are compartmentalized in HeLa cells. A...

SYNOPSIS. Attempts at continuous labeling of Crithidia fasciculata D.N.A with ["H]thymidine led to a pulse-chase situation due to a ccll-mediated conversion of thymidine to thymine in the medium. The uptake of ihymine was slow compared to that of thymidine. Neither the addition of deoxyadenosine nor the sequential addition of several aliquots of ['H] thymidine had an effect on the pattern of la...

Thymidine may act as an inducer of thymidine kinase activity in cells of higher plants. The general response is demonstrable in a randomly developing cell population such as is found in germinating wheat embryos. If a synchronously developing cell population is studied, however, potentially inducible cells are found to be susceptible to the inductive effect of thymidine only during about 10 per...

To determine the respective role of thymidine kinase and thymidylate synthase activities in the hyperoxia-induced decrease in DNA synthesis and their relationship with cell replication, we measured these two enzyme activities in primary cultures of porcine aortic endothelial cells under different O2 concentrations for various durations. In confluent cells, exposure to 95% O2 for 5 days reduced ...

The intraoellular concentration of thymidine triphosphate has been measured in thymine requiring mutants of Escherichia co&i K12 and E. coli 15, and compared with that in non-mutant strains using thymine, thymidine and a mixture of thymine and deoxyguenosine, in the growth medium. The data show (1) that the thymidine triphosphate concentration rises as the thymine concentration in the growth me...

The phosphorylation of thymidine and thymidylate to thymidine triphosphate, a proximal precursor of DNA, has been demonstrated repeatedly in extracts from a large variety of growing cells (2-7). A salient feature of a number of these studies was the surprising failure of one presumed intermediate, thymidine diphosphate, to accumulate in the reaction mixtures. Indeed, in several experiments wher...

Cytochalasin B (CB) shows a marked concentration-dependent inhibition of the incorporation of [(3)H]thymidine into Chinese hamster ovary cells. This inhibition was shown to result from an inhibition of thymidine uptake, not from an inhibition of DNA synthesis. Cells normally acquire the capacity to transport thymidine as they move from the G1 stage of the cell cycle into the S phase. If CB is a...

Cytochalasin B (CB) shows a marked concentration-dependent inhibition of the incorporation of [ 3H]thymidine into Chinese hamster ovary cells . This inhibition was shown to result from an inhibition of thymidine uptake, not from an inhibition of DNA synthesis . Cells normally acquire the capacity to transport thymidine as they move from the G1 stage of the cell cycle into the S phase . If CB is...

The effect of 17 beta-estradiol on cytoplasmic thymidine kinase activity was studied in MCF-7, a human breast cancer cell line in culture which responds to estrogens with an increase in the rate of growth. Levels of 17 beta-estradiol which maximally stimulate [3H]thymidine incorporation into DNA also maximally stimulate thymidine kinase activity. The Vmax for thymidine increased while the Km wa...