Guanine quadruplexes (G4s) are highly polymorphic four-stranded structures formed
within guanine-rich DNA and RNA sequences that play a crucial role in biological processes. The
recent discovery of the first G4 structures within mitochondrial DNA has led to a small revolution
in the field. In particular, the G-rich conserved sequence block II (CSB II) can form different types
of G4s that are thought to play a crucial role in replication. In this study, we decipher the most
relevant G4 structures that can be formed within CSB II: RNA G4 at the RNA transcript, DNA
G4 within the non-transcribed strand and DNA:RNA hybrid between the RNA transcript and the
non-transcribed strand.

Spectroscopic Characterization of Mitochondrial G-Quadruplexes

formed, but their topology changes from a less ordered to a highly ordered G4 when adding small
amounts of potassium or sodium cations. Circular dichroism was used to discriminate different
conformations and topologies of nucleic acids and was complemented with gel electrophoresis and
fluorescence spectroscopy studies.