Figure 6.

Graphical representation of the CANA letters assigned to DNA structures. Each phosphate group is enclosed with a colour-coded tetrahedron representing the assigned CANA letter: letter AAA is labelled red, BBB, 2B1 and 3B1 blue, BB2 yellow, miB green, ZZZ pink, steps with bases in the syn orientation orange and unassigned steps (NAN) grey. Steps that mix the features of two letters are composed of two colours: for example, a step mixing BII and A forms is shown in yellow/red. The sizes of the tetrahedrons represent the confal values for each step. The tetranucleotide with PDB entry 1ana (Conner et al., 1984 ▸) is a typical A-DNA, PDB entry 1bna (Drew et al., 1981 ▸) is B-DNA overall but with pronounced A-like features, PDB entry 362d (Harper et al., 1998 ▸) is a typical Z-­DNA, and PDB entry 190d (Chen et al., 1994 ▸) is DNA folded as an i-motif with several A-like steps but with most steps unassigned. The quadruplex with PDB entry 1jpq (Haider et al., 2002 ▸) has most steps in the B-DNA form; some steps have syn bases assigned (in orange) and a few are not assigned. The Holliday junction with PDB entry 1dcw (Eichman et al., 2000 ▸) is formed by four stems with a prevailing BII-DNA form; two steps at the junction have unstacked bases and are assigned the letter SQX (in violet), while just one step is not assigned. A tabular form of the NtC and CANA assignment of the steps in these six structures can be found in Supplementary Table S3; any DNA structure can be visualized at https://dnatco.org.