[
International Worm Meeting,
2021]
Intrinsically disordered domains are found in 30-40% of human proteins, many of which undergo liquid-liquid phase separation (LLPS). How these domains influence LLPS-mediated membraneless organelle (MLO) formation and organization in vivo is unclear. One such domain, consisting of Arginine and Glycine (RG/RGG) repeats, is critical for both P-granule and nucleolar function in C. elegans. We have identified 551 proteins with 3 or more regularly spaced RG/RGG repeats in C. elegans. Gene Ontology analysis reveals that these RG/RGG repeat-containing proteins are enriched in MLOs, including the nucleolus and P-granules. MEME motif discovery was used to identify a phenylalanine-rich RG/RGG motif typical of nucleolar proteins and a tyrosine-rich RG/RGG motif typical of P-granule proteins. These motifs were then used to predict the MLO localization of a highly abundant but uncharacterized protein, K07H8.10. The 176 amino acid-long RG/RGG repeat domain of K07H8.10 is the longest in C. elegans and is interspersed with phenylalanine, predicting nucleolar localization. In addition to its N terminal RG/RGG repeat domain, K07H8.10 contains a coiled-coil acidic domain and two C terminal RNA recognition motifs. Both the HHpred and the MARRVEL bioinformatics toolkits predict homology to Nucleolin, which contains these same three domains, although configured in a different arrangement in nematodes. We have fluorescently tagged K07H8.10 (now named NUCL-1) in the C. elegans germline and confirmed its nucleolar localization. Deleting the N terminal RG/RGG repeat domain of NUCL-1 results in fertile worms and does not impair NUCL-1 localization to the nucleolus. However, super resolution imaging of NUCL-1 in living worms reveals that sub-nucleolar compartmentalization of both NUCL-1 and Fibrillarin (FIB-1) are disrupted. Our results indicate that the NUCL-1 RG/RGG repeat domain is dispensable for localization to the nucleolus but is crucial for overall nucleolar organization.