Mutants of CHO cells resistant to the protein synthesis inhibitor emetine: Genetic and biochemical characterization of second-step mutants

Abstract

Second-step mutants highly resistant to the protein synthesis inhibitor emetine (Emt^RII) have been selected from emetine resistant (Emt^RI) Chinese hamster ovary cells described earlier. The frequency of the Emt^RII mutants was increased 50- to 75-fold after mutagenesis, and none of these highly resistant mutants could be selected in one step using wild-type cells. Like the Emt^RI mutants, the increased resistance of Emt^RII mutants results from another lesion in the polyribosomal fraction, as measured by the effects of emetine in fractionated extracts. As with the first-step mutants, the Emt^RII isolates behave recessively in somatic cell hybrids. Segregation studies have shown that the Emt^R lesions are not on the X chromosome, and in at least one isolate there is evidence that the Emt^RI and Emt^RII mutations may occur at different sites.