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. 2020 Jan 22;477(2):325–339. doi: 10.1042/BCJ20190703

Figure 4. Watson–Crick and Hoogsteen hydrogen bonds in triplex DNA molecules.

Figure 4.

A variety of triplex structures are shown involving three separate bases. The most common sequences, both in intramolecular and intermolecular triplexes, include A•A–T, G•G–C, and T•A–T for R•R–Y type triplexes (bottom left), and C+•G–C and T•A–T for Y•R–Y type triplexes. Each triplex includes two bases that form hydrogen bonds following the standard (Watson–Crick) pattern (red), plus one additional base form basepair where the interactions are stabilized by Hoogsteen pairing (green) [66]. Note that in some cases the additional hydrogen bonds are stabilized by positive charges on a cytosine base and, thus, are favoured at low pH.