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External IDsGeneCards: [1]
RefSeq (mRNA)



RefSeq (protein)



Location (UCSC)n/an/a
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View/Edit Human
pyrococcus horikoshii fibrillarin pre-rrna processing protein
Pfam clanCL0063

rRNA 2'-O-methyltransferase fibrillarin is an enzyme that in humans is encoded by the FBL gene.[1][2][3]


This gene product is a component of a nucleolar small nuclear ribonucleoprotein (snRNP) particle thought to participate in the first step in processing pre-ribosomal (r)RNA. It is associated with the U3, U8, and U13 small nucleolar RNAs and is located in the dense fibrillar component (DFC) of the nucleolus. The encoded protein contains an N-terminal repetitive domain that is rich in glycine and arginine residues, like fibrillarins in other species. Its central region resembles an RNA-binding domain and contains an RNP consensus sequence. Antisera from approximately 8% of humans with the autoimmune disease scleroderma recognize fibrillarin.[3]

Fibrillarin is a component of several ribonucleoproteins including a nucleolar small nuclear ribonucleoprotein (SnRNP) and one of the two classes of small nucleolar ribonucleoproteins (snoRNPs). SnRNAs function in RNA splicing while snoRNPs function in ribosomal RNA processing.

Fibrillarin is associated with U3, U8 and U13 small nuclear RNAs in mammals and is similar to the yeast NOP1 protein. Fibrillarin has a well conserved sequence of around 320 amino acids, and contains 3 domains, an N-terminal Gly/Arg-rich region; a central domain resembling other RNA-binding proteins and containing an RNP-2-like consensus sequence; and a C-terminal alpha-helical domain. An evolutionarily related pre-rRNA processing protein, which lacks the Gly/Arg-rich domain, has been found in various archaea.

A study by Schultz et al. indicated that the K-turn binding 15.5-kDa protein (called Snu13 in yeast) interacts with spliceosome proteins hPRP31, hPRP3, hPRP4, CYPH and the small nucleolar ribonucleoproteins NOP56, NOP58, and fibrillarin. The 15.5-kDa protein has sequence similarity to other RNA-binding proteins such as ribosomal proteins S12, L7a, and L30 and the snoRNP protein NHP2. The U4/U6 snRNP contains 15.5-kDa protein.[4] The 15.5-kDa protein also exists in a ribonucleoprotein complex that binds the U3 box B/C motif. The 15.5-kDa protein also exists as one of the four core proteins of the C/D small nucleolar ribonucleoprotein that mediates methylation of pre-ribosomal RNAs.

Structural evidence supporting the idea that fibrillarin is the snoRNA methyltransferase has been reviewed.[5]


Fibrillarin has been shown to interact with DDX5[6] and SMN1.[7]


  1. Aris JP, Blobel G (Feb 1991). "cDNA cloning and sequencing of human fibrillarin, a conserved nucleolar protein recognized by autoimmune antisera". Proceedings of the National Academy of Sciences of the United States of America. 88 (3): 931–5. doi:10.1073/pnas.88.3.931. PMC 50928. PMID 1846968.
  2. Jansen RP, Hurt EC, Kern H, Lehtonen H, Carmo-Fonseca M, Lapeyre B, Tollervey D (May 1991). "Evolutionary conservation of the human nucleolar protein fibrillarin and its functional expression in yeast". The Journal of Cell Biology. 113 (4): 715–29. doi:10.1083/jcb.113.4.715. PMC 2288999. PMID 2026646.
  3. 3.0 3.1 "Entrez Gene: FBL fibrillarin".
  4. Protein-Protein and Protein-RNA Contacts both Contribute to the 15.5K-Mediated Assembly of the U4/U6 snRNP and the Box C/D snoRNPs by Annemarie Schultz, Stephanie Nottrott, Nicholas James Watkins and Reinhard Lührmann in Molecular and Cellular Biology (2006) Volume 26, pages 5146–5154.
  5. The structure and function of small nucleolar ribonucleoproteins by Steve L. Reichow, Tomoko Hamma, Adrian R. Ferré-D'Amaré and Gabriele Varani in Nucleic Acids Research (2007) Volume 35, pages 1452–1464.
  6. Nicol SM, Causevic M, Prescott AR, Fuller-Pace FV (Jun 2000). "The nuclear DEAD box RNA helicase p68 interacts with the nucleolar protein fibrillarin and colocalizes specifically in nascent nucleoli during telophase". Experimental Cell Research. 257 (2): 272–80. doi:10.1006/excr.2000.4886. PMID 10837141.
  7. Pellizzoni L, Baccon J, Charroux B, Dreyfuss G (Jul 2001). "The survival of motor neurons (SMN) protein interacts with the snoRNP proteins fibrillarin and GAR1". Current Biology. 11 (14): 1079–88. doi:10.1016/S0960-9822(01)00316-5. PMID 11509230.
Human neuroblastoma, (SH-SY5Y) cells stained with antibody to fibrillarin in green, antibody to neurofilament NF-H in red and DNA in dark blue, The fibrillarin antibody binds to spots in the nucleus corresponding to nucleoli. The nucleoli also contain DNA and so appear as pale blue dots. The neurofilament NF-H antibody binds to cytoplasmic intermediate or 10nm filaments. Image, antibodies and staining by EnCor Biotechnology Inc.

Further reading