Germ granules are protein-RNA condensates that segregate with the embryonic germline. In C. elegans embryos, germ (P) granule assembly requires MEG-3, an intrinsically-disordered protein that forms RNA-rich condensates on the surface of PGL condensates at the core of P granules. MEG-3 is related to the GCNA family and contains an N-terminal disordered region (IDR) and a predicted ordered C-terminus featuring an HMG-like motif (HMGL). We find that MEG-3 is modular protein that uses its IDR to bind RNA and its C-terminus to drive condensation. The HMGL motif mediates binding to PGL-3 and is required for co-assembly of MEG-3 and PGL-3 condensates in vivo. Mutations in HMGL cause MEG-3 and PGL-3 to form separate condensates that no longer co-segregate to the germline or recruit RNA. Our findings highlight the importance of protein-based condensation mechanisms and condensate-condensate interactions in the assembly of RNA-rich germ granules.
All data generated or analyzed during this study are included in the manuscript and supporting files. Source data files have been provided for Figures 2-5.
- Helen Schmidt
- Andrea Putnam
- Dominique Rasoloson
- Geraldine Seydoux
The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.
- Robert H Singer, Albert Einstein College of Medicine, United States
© 2021, Schmidt et al.
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