Occurrence and classification of T-shaped interactions between nucleobases in RNA structures

Representation of (A) edges, (B) faces, (C) relative glycosidic orientations, and (D) identities of the horizontal rings participating in a T-shaped interaction. The “b” face of purines and the “a” face of pyrimidines is presented in panel A. σ_hv is the torsion angle involving the C1′ atom of the ribose sugar of the horizontal base, the centroid of ring (five-membered ring in purines and six-membered ring in pyrimidines) of the horizontal base, the centroid of ring of the vertical base and the C1′ atom of the ribose sugar of the vertical base. See Materials and Methods section for details.