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Description

rRNA 2'-O-methyltransferase fibrillarin (UniProt: P15646, also known as Histone-glutamine methyltransferase, U3 small nucleolar RNA-associated protein NOP1, Nucleolar protein 1, U3 snoRNA-associated protein NOP1) is encoded by the NOP1 (also known as LOT3, YDL014W, D2870) gene (Gene ID: 851548) in yeast. Fibrillarin is a nucleolar protein that is highly conserved throughout evolution. Human fibrillarin is 67% identical to its yeast homolog Nop1p. Fibrillarin is a protein component of C/D box small nucleolar ribonucleoproteins (snoRNPs) that direct 2 -O-methylation of rRNA and is also involved in other aspects of rRNA processing. Unlike snRNAs, which have a cytoplasmic phase of maturation, snoRNAs are restricted to the nucleus. Fibrillarin is essential for yeast viability and fibrillarin knockout is shown to be lethal in S. cerevisiae, however, expression of human or Xenopus fibrillarin overcome this lethality. The first 80 amino acids from the N terminal region of fibrillarin contain multiple RGG, or arginine-glycine-glycine (GAR). The remaining ~240 amino acids consist of the so called fibrillarin domain. NOP1 depleted strains of yeast are greatly impaired in the production of cytoplasmic ribosomes, and they have a reduced level of rRNA. Patients with scleroderma are reported to have strong circulating autoantibodies to fibrillarin. (Ref.: Tollervey, D et al. (1991). EMBO J. 10(3):573-83, Newton, K et al. (2003). Mol. Cell. Biol. 23(23): 8519-8527).