Figure 1.

Mammalian mtDNA from solid tissues is more sensitive to alkali than that of proliferating cultured cells. DNA from isolated mitochondria of human 143B cells, human placenta, murine LA9 cells and mouse liver was fractionated by 1D-AGE, after exposure to 100 mM sodium hydroxide (NaOH) for the indicated times, and blot hybridized to radiolabeled probes corresponding to segments of human (16 343–151) or murine (15 007–15 805) mtDNA. oc – open circlular, sc – supercolied, and ds – double stranded, ss – single stranded mtDNA. Treatments with type 2 RNase H fragmented the murine liver mtDNA to a similar extent (Supplementary Figure S1), indicating that most alkali sensitive sites are rNMPs and not abasic sites.