Diversity of capping basepairs and their conformations (bpC)† and dCC.

†Capping basepairs and their conformations are according to the Lee-Gutell system [39]: WC, Watson-Crick; Wb, wobble; S, sheared; rS, reversed sheared; fS, flipped sheared; pfS, parallel flipped sheared; H, Hoosteen; rH, reversed Hoogsteen; sWC, slipped Watson-Crick; sWb, slipped wobble; rWC, reversed Watson-Crick; rWb, reversed wobble; pS, parallel sheared.‡(3′, 5′) refers to the frequency of hetero capping basepair motifs (X:Y) whose Y is topologically located immediately 3′ and 5′ to a canonical helix, respectively.&The average dCC's for the canonical basepairs in the A-form RNA in T16S and H23S are 10.599 Å and 10.563 Å, respectively.