A Portal for Three-dimensional Structural Information about Nucleic Acids
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Saenger Legend*

The 28 possible base-pairs for A, G, U(T), and C involving at least two (cyclic) hydrogen bonds. Hydrogen and nitrogen atoms displayed as small and large filled circles, oxygen atoms as open circles, and glycosyl bonds and thick lines with R indicating ribose C1' atom. Base-pairs are boxed according to composition and symmetry, consisting of only purine, only pyrimidine, or mixed purine/pyrimidine pairs and asymmetric or symmetric base-pairs. Symmetry elements and are twofold rotation axes vertical to and within the plane of the paper. In the Watson-Crick base-pairs XIX and XX and in base-pairs VIII and XVIII, pseudosymmetry relating only glycosyl links but not individual base atoms is observed. Drawn after compilations in (33,457).

* W. Saenger (1984), Principles of Nucliec Acid Structure, 120-121. Springer-Verlag New York Inc., New York.