Cytoplasmically inherited mutations of a human cell line resulting in deficient mitochondrial protein synthesis

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Abstract
A large number of mutants deficient in mitochondrial protein synthesis (mtPS−) have been isolated from the human cell line VA2- B by subjecting cells partially depleted of their mtDNA to mutagenic treatments thought to be specific for mtDNA. Each of these mtPS− mutants has less than 10% of the wild- type rate of mitochondrial protein synthesis, exhibits reduced cytochrome oxidase and rutamycin-sensitive ATPase activities, requires high concentrations of glucose, and grows indefinitely in the presence of 100 μg/ml of chloramphenicol (CAP). Fusion of cytoplasts from seven mtPS− mutants to the nucleated thioguanine-resistant VA2-B derivative TG-6 has yielded numerous cybrid clones which grow in CAP plus thioguanine, whereas almost no clones have resulted from the fusion of nucleated mtPS− cells to TG- 6 cells: these results suggest that the gene(s) coding for the phenotype of mtPS− cells is localized in the cytoplasm (mtDNA?).