Figure 4.
Two stable clusters of hairpins are hotspots for mtDNA breakage. (A) A total of 189 reported 3′-breakpoints occur in the central hairpin (black circles) of a large cloverleaf-like structure (enclosed image) predicted for a 93-nt stretch (positions 16 028 to 16 120) of the control region near the tRNA-Pro (L-strand). Inside the hairpin, 144 breakpoints (19% of all of the 3′-breakpoints) are located on the 8-nt terminal loop. This deletion hotspot is located near the trinucleotide stop point (16 104–16 106; white circles) for the premature arrest of the H-strand synthesis responsible for forming a three-stranded DNA structure known as the displacement loop (D-loop). (B) All of the 5′-deletion breakpoints (n = 27) identified in the WANCY cluster of tRNAs are located in hairpin elements (L-strand). Most of them (n = 23) are located in a single stem–loop element predicted for the tRNA-Cys gene, downstream of the stem–loop structure that is associated with the origin of L-strand replication (OL).