Mutation assay at the thymidine kinase locus in diploid human lymphoblasts.

A thymidine kinase heterozygote was isolated from a diploid human lymphoblast line which forms colonies with high efficiency in microtiter dishes. We show that this cell line, called TK6, can be mutated from a TK+/- to TK-/- state by diverse mutagens, including ethyl methanesulfonate, butyl methanesulfonate, nitrosomethylurea, UV light, ICR-191, 4-nitroquinoline oxide, fluorodeoxyuridine, benzo[a]pyrene and aflatoxin B1. We report here the experiments required to demonstrate the applicability of this new line in quantitative assays of mutation in human cells. Mitotic recombination between the centromere and the tk locus could not be induced by either dimethylsulfoxide or phorbol-12-myristate-13-acetate.