Cycloheximide resistance in Chinese hamster cells. I. Spontaneous mutagenesis.

Resistance to cycloheximide (CHM) was studied in cultured Chinese hamster cells. Concentrations of CHM above 5-10-7 M were toxic for the cells. At concentrations above 9-10-7 M no colonies were recovered in selective medium. 15 resistant clones of independent origin were isolated in selective medium containing 7-10-7 M CHM. Resistance was stable when the cells were cultured under non-selective conditions. The spontaneous mutation rate was determined by the fluctuation test. Mutations to CHM resistance arose spontaneously. The spontaneous mutation rate to CHM resistance was about 10-5.