Phosphorylation-mediated RNA/peptide complex coacervation as a model for intracellular liquid organelles

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Biological cells are highly organized, with numerous subcellular compartments. Phosphorylation has been hypothesized as a means to control the assembly/disassembly of liquid-like RNA- and protein-rich intracellular bodies, or liquid organelles, that lack delimiting membranes. Here, we demonstrate that charge-mediated phase separation, or complex coacervation, of RNAs with cationic peptides can generate simple model liquid organelles capable of reversibly compartmentalizing biomolecules. Formation and dissolution of these liquid bodies was controlled by changes in peptide phosphorylation state using a kinase/phosphatase enzyme pair. The droplet-generating phase transition responded to modification of even a single serine residue. Electrostatic interactions between the short cationic peptides and the much longer polyanionic RNAs drove phase separation. Coacervates were also formed on silica beads, a primitive model for localization at specific intracellular sites. This work supports phosphoregulation of complex coacervation as a viable mechanism for dynamic intracellular compartmentalization in membraneless organelles.

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Figure 1: Illustrative representation and characterization of RNA/peptide coacervate systems.
Figure 2: Activity of LPP on the peptide and resulting phase separation.
Figure 3: Activity of PKA and dissolution of the coacervate phase.
Figure 4: Confocal microscopy of polyU/RRASLRRASL coacervates with fluorescent solutes.
Figure 5: Reversible coacervation modulated by changes in enzyme activity.


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This work was supported by the National Science Foundation (grant no. MCB-1244180). The authors thank P. Bevilacqua for discussions about RNA, including suggesting polyU RNA. The authors also thank D. Kirby for assisting with image analysis.

Author information

W.M.A. performed the experiments. W.M.A and C.D.K. conceived and designed the experiments, analysed the data and wrote the paper.

Correspondence to Christine D. Keating.

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The authors declare no competing financial interests.

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Aumiller, W., Keating, C. Phosphorylation-mediated RNA/peptide complex coacervation as a model for intracellular liquid organelles. Nature Chem 8, 129–137 (2016) doi:10.1038/nchem.2414

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