title: Esf2p, a U3-associated factor required for small-subunit processome assembly and compaction.
abstract: Esf2p is the Saccharomyces cerevisiae homolog of mouse ABT1, a protein previously identified as a putative partner of the TATA-element binding protein. However, large-scale studies have indicated that Esf2p is primarily localized to the nucleolus and that it physically associates with pre-rRNA processing factors. Here, we show that Esf2p-depleted cells are defective for pre-rRNA processing at the early nucleolar cleavage sites A0 through A2 and consequently are inhibited for 18S rRNA synthesis. Esf2p was stably associated with the 5' external transcribed spacer (ETS) and the box C+D snoRNA U3, as well as additional box C+D snoRNAs and proteins enriched within the small-subunit (SSU) processome/90S preribosomes. Esf2p colocalized on glycerol gradients with 90S preribosomes and slower migrating particles containing 5' ETS fragments. Strikingly, upon Esf2p depletion, chromatin spreads revealed that SSU processome assembly and compaction are inhibited and glycerol gradient analysis showed that U3 remains associated within 90S preribosomes. This suggests that in the absence of proper SSU processome assembly, early pre-rRNA processing is inhibited and U3 is not properly released from the 35S pre-rRNAs. The identification of ABT1 in a large-scale analysis of the human nucleolar proteome indicates that its role may also be conserved in mammals.
authors.affiliation: Fonds National de la Recherche Scientifique, Université Libre de Bruxelles, Institut de Biologie et de Médecine Moléculaires, Charleroi-Gosselies, Belgium.
authors.forename: Tran
authors.initials: T
authors.lastname: Hoang
authors.forename: Wen-Tao
authors.initials: WT
authors.lastname: Peng
authors.forename: Emmanuel
authors.initials: E
authors.lastname: Vanrobays
authors.forename: Nevan
authors.initials: N
authors.lastname: Krogan
authors.forename: Shawna
authors.initials: S
authors.lastname: Hiley
authors.forename: Ann L
authors.initials: AL
authors.lastname: Beyer
authors.forename: Yvonne N
authors.initials: YN
authors.lastname: Osheim
authors.forename: Jack
authors.initials: J
authors.lastname: Greenblatt
authors.forename: Timothy R
authors.initials: TR
authors.lastname: Hughes
authors.forename: Denis L J
authors.initials: DL
authors.lastname: Lafontaine
mesh_terms: D002466:Cell Nucleolus / Q000235:genetics / Q000378:metabolism; D002843:Chromatin / Q000235:genetics / Q000378:metabolism; D009687:Nuclear Proteins; D012323:RNA Processing, Post-Transcriptional; D012331:RNA, Fungal / Q000096:biosynthesis / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D012337:RNA, Ribosomal, 18S / Q000096:biosynthesis / Q000737:chemistry / Q000235:genetics; D012342:RNA, Small Nuclear / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D020537:RNA, Small Nucleolar / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D020718:Ribonucleoproteins, Small Nucleolar / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000166:cytology / Q000235:genetics / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism*; D014158:Transcription, Genetic
chemical_list: D002843:Chromatin; C502462:Esf2 protein, S cerevisiae; D009687:Nuclear Proteins; D012331:RNA, Fungal; D012337:RNA, Ribosomal, 18S; D012342:RNA, Small Nuclear; D020537:RNA, Small Nucleolar; D020718:Ribonucleoproteins, Small Nucleolar; D029701:Saccharomyces cerevisiae Proteins