RNA has the general ability to phase separate under specific in vitro conditions. The extend of the condensation propensity of RNA is heavily dependent on its sequence and ability to engage in inter/intra basepairing. This can be both Franklin-Crick and Hoogsteen basepairing.
Given the strong negative charge of the RNA backbone, RNA condensation requires the availability of strong counteranions. These can be Mg2+ or polycations (see coacervation). Condensation often requires also some form of molecular crowding (e.g., PEG).
Repeat RNAs implicated in human repeat expansion disorders (e.g., CUG repeats) are potent phase separators, and have also been used to form condensates in vivo (see TEARS).