Cytoplasmic Transfer of Chloramphenicol Resistance in Chinese Hamster Cells

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Abstract
Chloramphenicol [CAP] resistance, a dominant marker, is readily transferred between Chinese hamster cells by fusing enucleated cytoplasts from resistant cells to a sensitive recipient strain. Isolation of cytohybrids depends on complementary selection for recessive characteristics present in recipient cells, e.g., resistance to bromodeoxyuridine [BrdU]. Sources of background variation in this system were examined to determine the efficiency of cytoplasmic marker transfer. The frequency of mutants resistant to both CAP and BrdU was minimal in the parent strains used. Dual resistance arose by segregation within hybrids formed between nucleated cells present as contaminants in cytoplast fusion mixtures. Background variation may simulate cytoplasmic transfer of nuclear markers from donor cells (e.g., resistance to ouabain). Cytohybrids resistant to both ouabain and CAP were isolated from cytoplast fusion mixtures by selection with ouabain and BrdU. Such variants appeared to originate by mutation to ouabain resistance in recipient cells followed by cytoplasmic transfer of the CAP resistance marker.