PMC

Differential equivalence principle.

Time-temperature equivalence principle.

Scheme of an ellipsoidal inhomogeneity and the Eshelby equivalence principle.

RNA modularity and the three principles of equivalence. (a) The principle of isosteric equivalence exemplified by the RA motif constructed from its elemental submotifs. Watson–Crick (WC) base pairing is the basis for isosteric equivalence. The closing base pair (bp) on the GA minor is superimposable to the WC bps of the along-groove motif (overlaid with their electron densities in purple). The secondary structure and the stereo view of the RA motif are shown on the right. (b) The principle of structural equivalence as exemplified by the kink-turn motif. The kink-turn can take advantage of two different types of internal loops with different patterns of bps [GAA:gga (top) and loop E (bottom)]. The two types of kink-turns (GA-shared darker shade and loop E lighter) are shown overlaid in stereo (right). (c) The principle of topological/functional equivalence exemplified by three different RNA tectosquares. The individual motifs, the RA, the 3WJ, and the tRNA motif, while exhibiting completely different secondary structures and hydrogen-bonding patterns provide similar 90° bends that form the corner of the tectosquares.