Evolutionarily conserved structures in related
RNA molecules contain coordinated variations (covariations)
of paired nucleotides. Analysis of covariations is a very
powerful approach to deduce phylogenetically conserved
(i.e., functional) conformations, including tertiary interactions.
Here we discuss conserved RNA folding pathways that are
revealed by covariation patterns. In such pathways, structural
requirements for alternative pairings cause some nucleotides
to covary with two different partners. Such “coupled”
covariations between three or more nucleotides were found
in various types of RNAs. The analysis of coupled covariations
can unravel important features of RNA folding dynamics
and improve phylogeny reconstruction in some cases. Importantly,
it is necessary to distinguish between multiple covariations
determined by mutually exclusive structures and those determined
by tertiary contacts.