Abstract
Nucleophosmin (NPM1) is an abundant, oligomeric protein in the granular component of the nucleolus with roles in ribosome biogenesis. Pentameric NPM1 undergoes liquid-liquid phase separation (LLPS) via heterotypic interactions with nucleolar components, including ribosomal RNA (rRNA) and proteins which display multivalent arginine-rich linear motifs (R-motifs), and is integral to the liquid-like nucleolar matrix. Here we show that NPM1 can also undergo LLPS via homotypic interactions between its polyampholytic intrinsically disordered regions, a mechanism that opposes LLPS via heterotypic interactions. Using a combination of biophysical techniques, including confocal microscopy, SAXS, analytical ultracentrifugation, and single-molecule fluorescence, we describe how conformational changes within NPM1 control valency and switching between the different LLPS mechanisms. We propose that this newly discovered interplay between multiple LLPS mechanisms may influence the direction of vectorial pre-ribosomal particle assembly within, and exit from the nucleolus as part of the ribosome biogenesis process.
| Original language | English |
|---|---|
| Article number | 842 |
| Journal | Nature Communications |
| Volume | 9 |
| Issue number | 1 |
| DOIs | |
| State | Published - Dec 1 2018 |
Funding
Images were acquired at the Cell & Tissue Imaging Center which is supported by St. Jude Children’s Research Hospital (SJCRH) and NCI Cancer Center Support grant P30 CA021765. The small-angle X-ray scattering experiments were supported by DOE scientific user facilities. We thank Taehyung C. Lee for assistance with smFRET studies and Dr. Mylene Ferrolino and Nazia Ahmed for assistance with protein purification. This work was supported by funding from NIH 5RO1GM115634 (to R.W.K. and A.A.D.), an NCI Cancer Center Support grant (P30 CA21765 at SJCRH), NIH RO1 GM066833 (to A. A.D.), and ALSAC.