Fibrillarin

rRNA 2'-O-methyltransferase fibrillarin is an is_associated_with::enzyme that in humans is encoded by the FBL is_associated_with::gene.

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

Fibrillarin is associated with U3, U8 and U13 is_associated_with::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 is_associated_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. 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 is_associated_with::methyltransferase has been reviewed.

Interactions
Fibrillarin has been shown to interact with is_associated_with::DDX5 and is_associated_with::SMN1.