Common and distinctive features of GNRA tetraloops based on a GUAA tetraloop structure at 1.4 Å resolution

An interaction that mimics an A-minor motif. (A) Stereoview of the GUAA tetraloop (green) docking into the minor groove of a symmetry related stem region (red). The asterisk marks a solvent site that is conserved in tetraloop structures. The refined models of type I (B) and type II (C) A-minor contacts are superimposed on a 1.4 Å SIGMAA-weighted 2F_o–F_c electron density map. Weak C-H…O hydrogen bonds (as reviewed in Desiraju 1996) between C2 of A2662 and N3 of G2669 (3.2 Å) and between C2 of A2661 and O2 of C2652 (3.2 Å) may contribute to the stability of this A-minor interaction.