title: Splicing factor 2-associated protein p32 participates in ribosome biogenesis by regulating the binding of Nop52 and fibrillarin to preribosome particles.
abstract: Ribosome biogenesis starts with transcription of the large ribosomal RNA precursor (47S pre-rRNA), which soon combines with numerous factors to form the 90S pre-ribosome in the nucleolus. Although the subsequent separation of the pre-90S particle into pre-40S and pre-60S particles is critical for the production process of mature small and large ribosomal subunits, its molecular mechanisms remain undetermined. Here, we present evidence that p32, fibrillarin (FBL), and Nop52 play key roles in this separation step. Mass-based analyses combined with immunoblotting showed that p32 associated with 155 proteins including 31 rRNA-processing factors (of which nine were components of small subunit processome, and six were those of RIX1 complex), 13 chromatin remodeling components, and six general transcription factors required for RNA polymerase III-mediated transcription. Of these, a late rRNA-processing factor Nop52 interacted directly with p32. Immunocytochemical analyses demonstrated that p32 colocalized with an early rRNA-processing factor FBL or Nop52 in the nucleolus and Cajal bodies, but was excluded from the nucleolus after actinomycin D treatment. p32 was present in the pre-ribosomal fractions prepared by cell fractionation or separated by ultracentrifugation of the nuclear extract. p32 also associated with pre-rRNAs including 47S/45S and 32S pre-rRNAs. Furthermore, knockdown of p32 with a small interfering RNA slowed the early processing from 47S/45S pre-rRNAs to 18S rRNA and 32S pre-rRNA. Finally, Nop52 was found to compete with FBL for binding to p32 probably in the nucleolus. Given the fact that FBL and Nop52 are associated with pre-ribosome particles distinctly different from each other, we suggest that p32 is a new rRNA maturation factor involved in the remodeling from pre-90S particles to pre-40S and pre-60S particles that requires the exchange of FBL for Nop52.
authors.affiliation: Department of Applied Life Science, United Graduate School of Agriculture, Tokyo University of Agriculture and Technology, 3-5-8 Saiwai-cho, Fuchu-shi, Tokyo 183-8509, Japan.
authors.forename: Harunori
authors.initials: H
authors.lastname: Yoshikawa
authors.forename: Wataru
authors.initials: W
authors.lastname: Komatsu
authors.forename: Toshiya
authors.initials: T
authors.lastname: Hayano
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Miura
authors.forename: Keiichi
authors.initials: K
authors.lastname: Homma
authors.forename: Keiichi
authors.initials: K
authors.lastname: Izumikawa
authors.forename: Hideaki
authors.initials: H
authors.lastname: Ishikawa
authors.forename: Naoki
authors.initials: N
authors.lastname: Miyazawa
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Tachikawa
authors.forename: Yoshio
authors.initials: Y
authors.lastname: Yamauchi
authors.forename: Toshiaki
authors.initials: T
authors.lastname: Isobe
authors.forename: Nobuhiro
authors.initials: N
authors.lastname: Takahashi
mesh_terms: D001667:Binding, Competitive; D002352:Carrier Proteins / Q000378:metabolism*; D002460:Cell Line; D002466:Cell Nucleolus / Q000378:metabolism; D002868:Chromosomal Proteins, Non-Histone / Q000378:metabolism*; D020541:Coiled Bodies / Q000378:metabolism; D006801:Humans; D047468:Immunoprecipitation; D024101:Mitochondrial Proteins / Q000378:metabolism*; D009687:Nuclear Proteins / Q000378:metabolism*; D011485:Protein Binding; D025941:Protein Interaction Mapping; D021381:Protein Transport; D012322:RNA Precursors / Q000378:metabolism; D012323:RNA Processing, Post-Transcriptional; D016601:RNA-Binding Proteins / Q000378:metabolism; D012270:Ribosomes / Q000378:metabolism*; D013347:Subcellular Fractions / Q000378:metabolism
chemical_list: C087299:C1QBP protein, human; D002352:Carrier Proteins; D002868:Chromosomal Proteins, Non-Histone; D024101:Mitochondrial Proteins; D009687:Nuclear Proteins; D012322:RNA Precursors; D016601:RNA-Binding Proteins; C107468:RRP1 protein, human; C047458:fibrillarin