title: Bop1 is a mouse WD40 repeat nucleolar protein involved in 28S and 5. 8S RRNA processing and 60S ribosome biogenesis.
abstract: We have identified and characterized a novel mouse protein, Bop1, which contains WD40 repeats and is highly conserved through evolution. bop1 is ubiquitously expressed in all mouse tissues examined and is upregulated during mid-G(1) in serum-stimulated fibroblasts. Immunofluorescence analysis shows that Bop1 is localized predominantly to the nucleolus. In sucrose density gradients, Bop1 from nuclear extracts cosediments with the 50S-80S ribonucleoprotein particles that contain the 32S rRNA precursor. RNase A treatment disrupts these particles and releases Bop1 into a low-molecular-weight fraction. A mutant form of Bop1, Bop1Delta, which lacks 231 amino acids in the N- terminus, is colocalized with wild-type Bop1 in the nucleolus and in ribonucleoprotein complexes. Expression of Bop1Delta leads to cell growth arrest in the G(1) phase and results in a specific inhibition of the synthesis of the 28S and 5.8S rRNAs without affecting 18S rRNA formation. Pulse-chase analyses show that Bop1Delta expression results in a partial inhibition in the conversion of the 36S to the 32S pre-rRNA and a complete inhibition of the processing of the 32S pre-rRNA to form the mature 28S and 5.8S rRNAs. Concomitant with these defects in rRNA processing, expression of Bop1Delta in mouse cells leads to a deficit in the cytosolic 60S ribosomal subunits. These studies thus identify Bop1 as a novel, nonribosomal mammalian protein that plays a key role in the formation of the mature 28S and 5.8S rRNAs and in the biogenesis of the 60S ribosomal subunit.
authors.affiliation: Department of Molecular Genetics, University of Illinois at Chicago College of Medicine, Chicago, Illinois 60607-7170, USA.
authors.forename: Z
authors.initials: Z
authors.lastname: Strezoska
authors.forename: D G
authors.initials: DG
authors.lastname: Pestov
authors.forename: L F
authors.initials: LF
authors.lastname: Lau
mesh_terms: D000818:Animals; D002466:Cell Nucleolus / Q000378:metabolism; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D009154:Mutation; D012322:RNA Precursors / Q000378:metabolism; D012323:RNA Processing, Post-Transcriptional; D012335:RNA, Ribosomal / Q000235:genetics / Q000378:metabolism; D012339:RNA, Ribosomal, 28S / Q000235:genetics* / Q000378:metabolism; D012340:RNA, Ribosomal, 5.8S / Q000235:genetics* / Q000378:metabolism; D020449:Repetitive Sequences, Amino Acid; D012261:Ribonucleoproteins / Q000235:genetics / Q000378:metabolism; D012269:Ribosomal Proteins / Q000235:genetics / Q000378:metabolism; D012270:Ribosomes / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins
chemical_list: C116590:FLC1 protein, S cerevisiae; D005656:Fungal Proteins; D012322:RNA Precursors; D012335:RNA, Ribosomal; D012339:RNA, Ribosomal, 28S; D012340:RNA, Ribosomal, 5.8S; C075526:RNA, ribosomal, 12S; D012261:Ribonucleoproteins; D012269:Ribosomal Proteins; D029701:Saccharomyces cerevisiae Proteins; C039913:ribosomal protein S80