Structured RNAs enriched in dual-donating amines. (A) GNRA tetraloop receptor (cyan) bound to a GAAA tetraloop (green) from the P4–P6 domain with five dual-donating amines (PDB ID 1HR2). (B) Kink-turn from the SAM riboswitch with a 3 nt bulge (cyan) and series of sheared GA base pairs (green) with four dual-donating amines (PDB ID 2GIS). The stick representation on the right features only the sheared GA pairs. (C) Poly(A) strand (cyan) bound to the U-rich internal loop and GC closing base pair of an ENE (green) from a rice transposase mRNA with seven dual-donating amines (PDB ID 7JNH). For all panels, left is a cartoon representation, and right is a stick representation. Magenta dots highlighted in yellow depict H-bonds from dual-donating amines and gray dots depict other H-bonds. Cross-eye stereoviews are provided in Supplemental Figure S8, and the three structures are provided as Supplemental Structures S1–S3.
