SUMMARY
Intracellular condensation is a hallmark of many proteins containing intrinsically disordered regions (IDRs). Decoding the regulatory mechanisms of condensation encoded within the amino acid sequences of condensate-forming proteins is essential for understanding both how intracellular condensates assemble and how they contribute to various disease pathologies. Here, we investigated the budding yeast P-body proteins Nst1 and Edc3, which exhibit pronounced intracellular self-condensation, and identified charged amino acid clusters in the low complexity regions (LCRs) that modulate their phase behavior. Guided by the stickers-and-spacers framework, we hypothesized that clusters of charged residues within IDRs function in promoting intracellular condensation process. Using a sliding-window approach, we designated and dissected the polyelectrolyte (PE) domains of Nst1 and Edc3 and established their essential contributions to condensate coalescence. In Nst1, the polyanionic (PA) subdomain enhances intermolecular attraction and promotes coalescence, whereas the polyampholyte (PAM) subdomain imparts rigidity to the condensate as a distinct modulatory element and functions as a platform in condensation process of other P-body components. PA of Edc3 also regulates coalescence. Extending these findings to the neurodegenerative disease-associated protein TDP-43, we show that its PA regions are critical for coalescence, consistent with the presence of negatively charged amino acid clusters as potent molecular stickers functioning in condensate coalescence in cells. These results highlight charged-residue clusters as important sequence determinants of protein phase behavior and suggest that they represent promising novel regulatory targets for modulating TDP-43 condensation in cells.