A mechanism for MEX-5-driven disassembly of PGL-3/RNA condensates in vitro.

Lewis, Natasha S; Zedlitz, Silja; Ausserwöger, Hannes; McCall, Patrick M; Hubatsch, Lars; Nousch, Marco; Ruer-Gruß, Martine; Hoege, Carsten et al. · Proc Natl Acad Sci U S A · 2025

basic_science · Level V

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Abstract

MEX-5 regulates the formation and dissolution of P granules in <i>Caenorhabditis elegans</i> embryos, yet the thermodynamic basis of its activity remains unclear. Here, using a time-resolved in vitro reconstitution system, we show that MEX-5 dissolves preassembled liquid-like PGL-3/RNA condensates by altering RNA availability and shifting the phase boundary. We develop a microfluidic assay to systematically analyze how MEX-5 influences phase separation. By measuring the contribution of PGL-3 to phase separation, we show that MEX-5 reduces the free energy of PGL-3, shifting the equilibrium toward dissolution. Our findings provide a quantitative framework for understanding how RNA-binding proteins modulate condensate stability and demonstrate the power of microfluidics in precisely mapping phase transitions.

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