Analysis of Replication Intermediates Indicates That Drosophila melanogaster Mitochondrial DNA Replicates by a Strand-Coupled Theta Mechanism
Figure 1
Schematic representation of the mitochondrial genome of D. melanogaster, showing major replication intermediates.
A) Positions of unique restriction enzyme recognition sites in D. melanogaster mtDNA used in this study. Thick black line represents the NCR, arrow denotes the proposed direction of replication from the putative origin. Positions of probes used in this study are shown as bold lines. B) Diagram showing maximum spans of expected 2DNAGE migration arcs of major replication intermediates, following linearization of mtDNA with a generic restriction enzyme: b – bubble arc, Y – Y or Y-like arc (created by strand breakage of bubble or double Y species at the fork or origin), X – colliding forks and Holliday junctions, dY – double Y-arc, ey – “eyebrow” arc, sub-b – sub-bubble arc (bubble structures with ssDNA regions), uc – uncut circles, 1N - linearized non-replicating DNA (unit-length mitochondrial genome). Bold line extending from 1N spot marks the region where Y and dY structures migrate together. Schematic representation of expected intermediates generated by MbiI and BshNI digestions in case of unidirectional strand-coupled replication are shown in panels C and D, respectively.