X-Ray induced mutation and DNA repair in mammalian cells

From the original L5187Y cell line, a number of mutants of different radiosensitivity was available. The frequency of X-ray induced thymidine resistant variants in the L 5178Y cell line was compared with that in its more radiosensitive mutants by means of a newly developed assay system using thymidine as selective agent. The amount of excision repair in the cell lines has also been measured. The data indicate that the most radiosensitive cell line is by far the most sensitive to mutation induction and that mutability decreases as sensitivity decreases. No correlation was found between levels of repair replication and cellular sensitivity, indicating that there is probably no relationship between mutability and the amount of repair replication in these cell lines. (G.G.)