Figure 5.

Schema of the polymorphic, or multi-well, landscape exhibited by B-DNA at the tetranucleotide level expressed in the purine (R)/pyrimidine (Y) alphabet, for which only 10 distinct combinations exist, but which still distinguish all possible behaviors. The only helical coordinates that exhibited multi-modality are shift, slide and twist, and each junction in the figure is marked with which coordinates can be multi-modal in it. There is a very high correlation between the occurrence of multi-modality and the formation of a noncanonical hydrogen bond in either the same or a neighboring junction, along with its associated BI/BII backbone transition (see text).