Distinct regions of the intrinsically disordered protein MUT-16 mediate assembly of a small RNA amplification complex and promote phase separation of Mutator foci.

• Main Authors: Celja J Uebel, Dorian C Anderson, Lisa M Mandarino, Kevin I Manage, Stephan Aynaszyan, Carolyn M Phillips
• Format: Article
• Language: English
• Published: Public Library of Science (PLoS) 2018-07-01
• Series: PLoS Genetics
• Online Access: http://europepmc.org/articles/PMC6072111?pdf=render

In C. elegans, efficient RNA silencing requires small RNA amplification mediated by RNA-dependent RNA polymerases (RdRPs). RRF-1, an RdRP, and other Mutator complex proteins localize to Mutator foci, which are perinuclear germline foci that associate with nuclear pores and P granules to facilitate small RNA amplification. The Mutator complex protein MUT-16 is critical for Mutator foci assembly. By analyzing small deletions of MUT-16, we identify specific regions of the protein that recruit other Mutator complex components and demonstrate that it acts as a scaffolding protein. We further determine that the C-terminal region of MUT-16, a portion of which contains predicted intrinsic disorder, is necessary and sufficient to promote Mutator foci formation. Finally, we establish that MUT-16 foci have many properties consistent with a phase-separated condensate and propose that Mutator foci form through liquid-liquid phase separation of MUT-16. P granules, which contain additional RNA silencing proteins, have previously been shown to have liquid-like properties. Thus, RNA silencing in C. elegans germ cells may rely on multiple phase-separated compartments through which sorting, processing, and silencing of mRNAs occurs.