Effect of mitochondrial dosage on transfer of chloramphenicol resistance

Enucleated chloramphenicol-resistant (CAP^r) AMT cytoplasts were labeled with the mitochondrial-specific fluorophore rhodamine 123 (R-123) and fused to CAP-sensitive (CAP^s) 984 whole cells. Using the fluorescence-activated cell sorter (FACS), the cybrids were separated on the basis of the amount of CAP^r donor mitochondria which they received. The cybrids were then selected in the presence of various concentrations of CAP to examine the effect of donor mitochondrial dosage on the transfer of CAP resistance. Those cybrids which received the greatest amount of CAP^r mitochondria (as determined using the FACS) were found to be approximately 3-fold more resistant to CAP selection than cybrids which had received fewer donor mitochondria. In addition, those cybrids which initially received the greatest CAP^r mitochondrial dosage remained more stably resistant to subsequent selection in CAP. These results indicate that the amount of donor mitochondria the cybrid receives may be important in determining the expression of mitochondrial specific markers.