DIFFERENT CELLULAR BACKGROUNDS CONFER A MARKED ADVANTAGE TO EITHER MUTANT OR WILD-TYPE MITOCHONDRIAL GENOMES

After the introduction of mitochondria with a mixture of mutant and wi ld-type mitochondrial DNA (mtDNA) into a human rho degrees cell line ( 143B,206), Yoneda ct al, [Yoneda, M., Chomyn, A., Martinuzzi, A., Hurk o, O, and Attardi, G, (1992) Proc. Natl. Acad. Sci. USA 89, 11164-1116 8] observed a shift in the proportion of the two mitochondrial genotyp es in a number of cybrid clones, In every case where a shift was obser ved, there was an increase in the proportion of mutant mtDNA, By using the same cell line (143B,206 rho degrees), we also generated cybrids that were either stable in their mitochondrial genotype or showed an i ncrease in the proportion of mutant mtDNA. However, temporal analysis of the same mutant mtDNA type in another rho degrees cell line reveale d a quite distinct outcome. Those clones that showed a change shifted toward higher levels of wild-type rather than mutant mtDNA, These resu lts indicate that the nuclear genetic background of the recipient (rho degrees) cell can influence the segregation of mutant and wild-type m itochondrial genomes in cell cybrids.