Dynamics and tetraloop-tetraloop receptor (TL/TLR) tertiary motif assembly. (A) The crystal structure of the P4–P6 domain of the Tetrahymena ribozyme with its TL/TLR highlighted in blue (PDB: 1GID [48]; left panel) and an overlay of the free (yellow, PDB: 1TLR [49]) and bound (blue, PDB: 1GID [48]) forms of the TLR (top) and the free (yellow, PDB: 1ZIF [50]) and bound (blue, PDB: 1GID [48]) forms of the TL (bottom) (right panel). (B) TL/TLR constructs used in single molecule FRET experiments [adapted from 53]. (C) Predicted free energy reaction profile for the formation of a tertiary contact based on functional measurements made on inter- and intramolecular tertiary contacts [51,52], as described in the text.