Summary
RNA-protein (RNP) granules are non-membrane bound organelles with enigmatic roles in RNA metabolism. Metazoa contain RNP “germ granules” specialized for germline development. Caenorhabditis elegans P-granules are liquid droplet germ granules that require PGL proteins for assembly. Here we investigate PGL proteins to understand the relationship between P-granule assembly and germline function. We determine the crystal structure of a PGL N-terminal domain (NTD) and find that it dimerizes. From the structure, we identify mutations that disrupt PGL dimerization in vitro and prevent PGL granule formation in mammalian cells in culture. These same mutations in nematodes prevent assembly of PGL into P-granules and cause sterility. Using a protein-mRNA tethering assay, we show that mRNAs recruited to PGL-1 are repressed, while mRNAs recruited to PGL-1 mutants defective for granule assembly are expressed. Therefore, the effects of PGL on mRNA repression and fertility are tightly linked to its formation of higher-ordered assemblies.
- Abbreviations
- RNA
- ribonucleic acid
- UTR
- untranslated region
- GFP
- green fluorescent protein
- CRISPR
- Clustered Regularly Interspaced Short Palindromic Repeats