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Protein FBL PDB 2ipx.png
PDB rendering based on 2ipx.
Available structures
PDB Ortholog search: PDBe, RCSB
Symbols FBL ; FIB; FLRN; RNU3IP1
External IDs OMIM134795 MGI95486 HomoloGene1099 GeneCards: FBL Gene
RNA expression pattern
PBB GE FBL 211623 s at tn.png
More reference expression data
Species Human Mouse
Entrez 2091 14113
Ensembl ENSG00000105202 ENSMUSG00000046865
UniProt P22087 P35550
RefSeq (mRNA) NM_001436 NM_007991
RefSeq (protein) NP_001427 NP_032017
Location (UCSC) Chr 19:
40.33 – 40.34 Mb
Chr 7:
28.17 – 28.18 Mb
PubMed search [1] [2]
PDB 1g8a EBI.jpg
pyrococcus horikoshii fibrillarin pre-rrna processing protein
Symbol Fibrillarin
Pfam PF01269
Pfam clan CL0063
InterPro IPR000692
SCOP 1fbn

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 nuclear 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 archaebacteria.

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 small nucleolar ribonucleoprotein methyltransferase has been reviewed.[5]


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


  1. ^ Aris JP, Blobel G (March 1991). "cDNA cloning and sequencing of human fibrillarin, a conserved nucleolar protein recognized by autoimmune antisera". Proc. Natl. Acad. Sci. U.S.A. 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 (June 1991). "Evolutionary conservation of the human nucleolar protein fibrillarin and its functional expression in yeast". J Cell Biol 113 (4): 715–29. doi:10.1083/jcb.113.4.715. PMC 2288999. PMID 2026646. 
  3. ^ a b "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, S M; Causevic M; Prescott A R; Fuller-Pace F V (June 2000). "The nuclear DEAD box RNA helicase p68 interacts with the nucleolar protein fibrillarin and colocalizes specifically in nascent nucleoli during telophase". Exp. Cell Res. (UNITED STATES) 257 (2): 272–80. doi:10.1006/excr.2000.4886. ISSN 0014-4827. PMID 10837141. 
  7. ^ Pellizzoni, L; Baccon J; Charroux B; Dreyfuss G (July 2001). "The survival of motor neurons (SMN) protein interacts with the snoRNP proteins fibrillarin and GAR1". Curr. Biol. (England) 11 (14): 1079–88. doi:10.1016/S0960-9822(01)00316-5. ISSN 0960-9822. PMID 11509230. 

Further reading[edit]