Genetic complementation in hybrid cells derived from mutagen-induced 6-thioguanine-resistant Chinese hamster cells.

6-Thioguanine(6TG)-resistant clones were obtained in Chinese hamster cells after treatment with ethyl methanesulfonate (EMS) or N-methyl-N'-nitro-N nitrosoguanidine (MNNG). These 6TG-resistant clones were tested for their complementation ability using cell hybridization method with polyethylene glycol. Among twenty-seven EMS-induced 6TG-resistant clones, six were shown to be complementable with a standard CH 252 clones (group A) and classified as complementation group B. Among fifteen MNNG-induced 6TG-resistant clones, three were classified as group A and ten as group B. Further hybridization tests within the same complementation group showed that there were no subgroups in each complementation group. These results indicate that the chemicals used for the induction of forward mutations may have affected different cistrons in the hypoxanthine-guanine phosphoribosyltransferase locus in cultured Chinese hamster cells.