Fibrillarin is a highly conserved nucleolar methyltransferase responsible for ribosomal RNA methylation across evolution from Archaea to humans. It has been reported that fibrillarin is involved in the methylation of histone H2A in nucleoli and other processes, including viral progression, cellular stress, nuclear shape, and cell cycle progression. We show that fibrillarin has an additional activity as a ribonuclease. The activity is affected by phosphoinositides and phosphatidic acid and insensitive to ribonuclease inhibitors. Furthermore, the presence of phosphatidic acid releases the fibrillarin-U3 snoRNA complex. We show that the ribonuclease activity localizes to the GAR (glycine/arginine-rich) domain conserved in a small group of RNA interacting proteins. The introduction of the GAR domain occurred in evolution in the transition from archaea to eukaryotic cells. The interaction of this domain with phospholipids may allow a phase separation of this protein in nucleoli.

• Keywords
• fibrillarin, nucleolus, phosphoinositides, rRNA, ribonucleolar particle, viral progression,
• MeSH
• Chromosomal Proteins, Non-Histone chemistry   genetics   metabolism   MeSH
• Phospholipids metabolism   MeSH
• HeLa Cells MeSH
• Humans MeSH
• RNA, Small Nucleolar metabolism   MeSH
• Mutation genetics   MeSH
• Protein Domains MeSH
• Recombinant Proteins metabolism   MeSH
• Ribonucleases chemistry   genetics   metabolism   MeSH
• Ribonucleoproteins metabolism   MeSH
• Structure-Activity Relationship MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Chromosomal Proteins, Non-Histone MeSH
• fibrillarin MeSH Browser
• Phospholipids MeSH
• RNA, Small Nucleolar MeSH
• Recombinant Proteins MeSH
• Ribonucleases MeSH
• Ribonucleoproteins MeSH
• RNA, U3 small nucleolar MeSH Browser