Detection of mutant diphtheria toxin-resistant Chinese hamster lung cells in situ by autoradiography.

An autoradiographic method was developed to detect diphtheria toxin-resistant (DTr) Chinese hamster lung cells in situ. With this method, a dose-dependent increase in the number of DTr cells was observed after exposure of the cells to increasing concentrations of ethyl methanesulfonate (EMS). Segregation of EMS-induced DTr cells in a sector of single colonies was clearly demonstrated. It was also found by this method that the number of DTr cells induced by a fixed concentration of EMS was not determined by the number of cell divisions during the expression time but by the period after exposure of the cells to EMS.