ISOLATION AND CHARACTERIZATION OF THYMIDINE TRANSPORT MUTANTS OF CHINESE HAMSTER CELLS

In this paper a new system of checking mutation frequencies of the incorporation variety for cells in culture was presented. The mutation rate of a mutation in the thymidine incorporating system was determined by the fluctuation test to be 2.6 × 10-4 mutants/cell/generation. A cell line mutant for thymidine transport was isolated and studied by autoradiographic staining technique. Thymidine kinase was assayed in normal and Tp- cell lines and both were found to have substantial enzyme activity. Incorporation studies were performed to demonstrate the specific and facilitative nature of thymidine uptake by cells. From the results presented, it is clear that the thymidine incorporation system of Chinese hamster cells suffers a high rate of spontaneous mutation. Some of the mutations in the thymidine incorporation system of these cells are at the level of the thymidine transport system. © 1969.