PMID:10891491

Citation	Strezoska, Z, Pestov, DG and Lau, LF (2000) Bop1 is a mouse WD40 repeat nucleolar protein involved in 28S and 5. 8S RRNA processing and 60S ribosome biogenesis. Mol. Cell. Biol. 20:5516-28
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.
Links	PubMed PMC86002
Keywords	Animals; Cell Nucleolus/metabolism; Fungal Proteins/genetics; Fungal Proteins/metabolism; Mice; Mutation; RNA Precursors/metabolism; RNA Processing, Post-Transcriptional; RNA, Ribosomal/genetics; RNA, Ribosomal/metabolism; RNA, Ribosomal, 28S/genetics; RNA, Ribosomal, 28S/metabolism; RNA, Ribosomal, 5.8S/genetics; RNA, Ribosomal, 5.8S/metabolism; Repetitive Sequences, Amino Acid; Ribonucleoproteins/genetics; Ribonucleoproteins/metabolism; Ribosomal Proteins/genetics; Ribosomal Proteins/metabolism; Ribosomes/genetics; Ribosomes/metabolism; Saccharomyces cerevisiae Proteins
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