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. Author manuscript; available in PMC: 2019 Feb 23.
Published in final edited form as: Trends Genet. 2018 Dec 4;35(2):129–144. doi: 10.1016/j.tig.2018.11.001

Figure 1. The G4 Topology.

Figure 1

(A) Hoogsteen base pairing gives self-assembly of G-tetrads [assisted by metal (M) ions] in sequences with repetitive G tracts (G-stem). (B) These G-tetrads are separated by stretches of nucleotides called ‘loops’ (L). Two or more G-tetrads form DNA secondary structure G-quadruplex (G4) DNA. (C) Different topologies in which G4s usually exist in intra-molecular and inter-molecular forms. (D) Schematic showing typical circular dichroism (CD) spectral signatures of parallel and anti-parallel G-quadruplexes (G4s).