Liquid-liquid phase separation (LLPS) of multivalent biopolymers is a ubiquitous process in biological systems and is of importance in bio-mimetic soft matter design. The phase behavior of biomolecules, such as...
Co-phase separation of RNAs and RNA-binding proteins is thought to drive the biogenesis of ribonucleoprotein granules. RNAs can also undergo phase transitions in the absence of proteins. However, the physicochemical driving forces of protein-free RNA-driven phase transitions remain unclear. Here, we report that RNAs of various types undergo phase transitions with system-specific lower critical solution temperatures. This entropically-driven phase behavior requires Mg2+ions and is an intrinsic feature of the phosphate backbone that is modulated by RNA bases. RNA-only condensates can additionally undergo a temperature-dependent percolation transition, which is enabled by a combination of Mg2+-dependent bridging interactions among phosphate groups and RNA base-stacking / base-pairing. Phase separation coupled to percolation can cause dynamical arrest of RNAs within condensates. The dynamical arrest of condensates formed by the RNase P ribozyme suppresses its catalytic activity. Our work highlights the need to incorporate RNA-driven phase transitions into models for RNP granule biogenesis.
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