Mouse Monoclonal Antibody to Nop1p Cat# MCA-28F2

      Nop1p was originally identified as a nucleolar protein of bakers yeast, Saccharomyces cerevisiae(accession P15646). The Nop1p protein is essential for yeast viability and is localized in the nucleoli. The human homologue of Nop1p is fibrillarin (accession P22087) a component of the nucleolar small nuclear ribonucleoprotein (snRNP) particle. The human fibrillarin gene is located on chromosome 19 (19q13.1). Fibrillarin proteins have been cloned and sequenced from several other species (Mouse, accession P35550, Xenopus accession P22232, C. elegans accession Q22053, and S. pombe accession P35551. You can download a pdf of the sequence alignment here.

      The N terminal ~80 amino acids contain multiple copies based on the peptide RGG, and the remaining ~240 amino acids consist of the fibrillarin domain. A fibrillarin homologue has also been identified in the genome of the archean Methanococcus (accession NC_000909). This protein lacks the RGG rich N-terminal extension but is clearly homologues to the other sequences throughout all of the fibrillarin domain. The structure of this molecule has been determined and shown to consist of 2 extended b-sheets flanked by 4 a-helixes (Medline link).
Patients with the autoimmune disease scleroderma often have circulating autoantibodies to a 34 kDa protein which was subsequently found to be fibrillarin.

      To raise this antibody, mice were injected with yeast nuclear preparations and hybridomas were screened by immunofluorescence on yeast cells and by western blotting on yeast protein homogenates. This monoclonal antibody does not cross-react with fibrillarin in other species, but is an excellent marker of the nucleolus of yeast cells. For Nop1p/fibrillarin visualization in vertebrates, Drosophila and C. elegans and other species we recommend MCA-38F3, also available from EnCor.

      Antibody is supplied as a concentrated tissue culture supernatant, sterile-filtered, from an Integra CL-350 biochamber plus sodium azide. The immunoglobulin subtype is IgG3. The concentration of IgG is unknown. Store at 4°C or -20°C. For western blots of yeast protein samples, use MCA-28F2 diluted 1/10,000 (cell lysates) to 1/25,000 (nuclear fractions), followed by chemiluminescent detection (ECL). See here for image of blot. For other (non-ECL) western detection methods, try MCA-28F2 diluted 1/1000 to 1/5000. For immunofluorescence on yeast cells, use MCA-28F2 diluted 1/2000 to 1/20,000. We routinely dilute to 1/5000. For immunoprecipitations, use 2-4 µl for an amount of lysate derived from 5 OD600 units of yeast culture.

      This antibody has been tested on formalin fixed and paraffin embedded samples for IHC, and is not recommended for this purpose. For this purpose we recommend another EnCor antibody MCA-4A4.

1. Aris JP and Blobel G. Identification and characterization of a yeast nucleolar protein that is similar to a rat liver nucleolar protein. J. Cell Biol. 107:17-31 (1988).
2. Aris JP and Blobel G. cDNA cloning and sequencing of human fibrillarin, a conserved nucleolar protein recognized by autoimmune antisera. Proc. Natl. Acad. Sci. 88:931-5 (1991).
3. Ochs RL, Lischwe MA, Spohn WH, Busch H. Fibrillarin: a new protein of the nucleolus identified by autoimmune sera. Biol. Cell. 54:123-33 (1985).
4. Newton K, Petfalski E, Tollervey D, Caceres JF. Fibrillarin is essential for early development and required for accumulation of an intron-encoded small nucleolar RNA in the mouse. Mol. Cell Biol. 23:8519-27 (2003).
5. Okano Y, Steen VD, Medsger TA. Autoantibody to U3 nucleolar ribonucleoprotein (fibrillarin) in patients with systemic sclerosis. Arth. Rheum. 35:95-100 (1992).