Amine-acceptor pair measurements to determine H-bonding criteria. (A) Heat map depicting amine-acceptor geometries. Because of their dominance from canonical base pairs, A(N6)–U(O4), C(N4)–G(O6), G(N2)–C(O2), and G(N2)–C(N3) pairs are not included. Any pairs with distance and angle measurements that fall within the dashed red box are considered H-bonding. The points colored gray have counts beyond the maximum of the color scale. (B,C) Examples that meet and do not meet criteria. The angle and distance are shown for each interaction that involves an amine. (B) Depiction of a GA base pair from chain a in PDB ID 7UW1 involving G91 and A76 (Morgan et al. 2023). Magenta: amine interaction that falls within the dashed red box. Blue: amine interaction that falls outside the dashed red box. Gray: an interaction that does not involve an amine and thus is not included. (C) Depiction of a stacked AG from the same chain involving A1173 and G1174. Orange: amine interaction that falls outside the dashed red box.
