(B) Repeated recloning of P29 subclones to select the subclone with the highest proportion of T15091C mtDNA. A subclone P29-22 with 22% T15091C mtDNA was cultivated for 2 months to allow its stochastic segregation. From this clone, we obtained 34 subclones; the one with the most prevalent T15091C mtDNA possessed 34% T15091C mtDNA. After four more rounds of subcloning, we isolated five P29 subclones with more than 95% T15091C mtDNA, and one of them was used as
P29-95. (C) Identification and quantification of T15091C mtDNA with an additional G9976A mutation in the ND4L gene in subclone P29-95 by BstNI digestion of the PCR products.
The mtDNA without the G9976A mutation produced 108-bp and 32-bp fragments owing to the presence of the BstNI site, whereas mtDNA with the G99976A mutation produced a
140-bp fragment owing to the loss of the BstNI site by mutation. About 55% of T15091C mtDNA possessed the additional G9976A mutation, whereas mtDNA without the T15091C
mutation did not possess the G9976A mutation.