Figure 2.

Electron microscopy of mtDNA replication intermediates isolated from control and mtDNA helicase-overexpressing Schneider S2 cells. (A) Representative electron microscopic images of circular (full-length (∼6 μm), left panel) and theta replication intermediate (right panel, indicated by the white arrow) mtDNA molecules obtained from control S2 cells. Scale bars 200 nm. (B) Representative electron microscopic images of circular (left panel; full-length (∼6 μm, upper molecule) and deleted (∼5 μm, lower molecule)) and theta replication intermediate (right panel, indicated by the white arrow; deleted, (∼5.6 μm)) mtDNA molecules obtained from mtDNA helicase-overexpressing S2 cells. Scale bars 200 nm. (C) EM quantification of mtDNA theta replication intermediates obtained from control and helicase-overexpressing S2 cells expressed as percentage of total monomeric mtDNA circles. The analysis was performed in three independent experiments with duplicate samples in each group. 3730 and 459 molecules were scored in control and helicase-overexpressing mtDNA samples, respectively. Statistical analysis was performed using the non-parametric Mann–Whitney U-Test and the data are presented as mean values. A P-value <0.05 was considered statistically significant.