RNA-Polycation complex: too strong a binding

Polyelectrolyte coacervate droplets, formed by liquid-liquid phase separation of oppositely charged macromolecules such as RNA, proteins, and synthetic polyelectrolytes, are sensitive to salts in the solution. The addition of salts leads to electrostatic screening of charges on macromolecules, decreasing macromolecular interactions, and, above a certain salt concentration, the droplets disappear as the system transitions from a two-phase to a single-phase state. We found that in coacervates of RNA and polycations, the two oppositely charged macromolecules remain bound to each other even in the single-phase region. This binding persisted even at very high salt concentrations (NaCl). We attribute this behavior to strong electrostatic interactions that persist at even a significantly reduced Debye length. We found that this polycation-bound RNA creates challenges in RNA folding (and subsequent ribozyme catalysis) and separation (gel electrophoresis). Surprisingly, the addition of an excess of synthetic polyanions rescued the RNA, allowing its proper folding as well as separation via gel electrophoresis. We wonder whether cells have mechanisms to free RNA from bound polycations to enable its proper functioning, and whether disruption of polycation regulation leads to RNA-associated diseases.