title: Structural and functional analysis of Utp23, a yeast ribosome synthesis factor with degenerate PIN domain.
abstract: During synthesis of yeast ribosome, a large complex, called the 90S pre-ribosome or the small subunit processome, is assembled on the nascent precursor rRNA and mediates early processing of 18S rRNA. The Utp23 protein and snR30 H/ACA snoRNA are two conserved components of 90S pre-ribosomes. Utp23 contains a degenerate PIN nuclease domain followed by a long C-terminal tail and associates specifically with snR30. Here, we report the crystal structure of the Utp23 PIN domain at 2.5-Å resolution. The structure reveals a conserved core fold of PIN domain with degenerate active site residues, a unique CCHC Zn-finger motif, and two terminal extension elements. Functional sites of Utp23 have been examined with conservation analysis, mutagenesis, and in vivo and in vitro assays. Mutations in each of three cysteine ligands of zinc, although not the histidine ligand, were lethal or strongly inhibitory to yeast growth, indicating that the Zn-finger motif is required for Utp23 structure or function. The N-terminal helix extension harbors many highly conserved basic residues that mostly are critical for growth and in vitro RNA-binding activity of Utp23. Deletion of the C-terminal tail, which contains a short functionally important sequence motif, disrupted the interaction of Utp23 with snR30 and perturbed the pre-ribosomal association of Utp23. Our data establish a structural framework for dissecting Utp23 function in the assembly and dynamics of 90S pre-ribosomes.
authors.forename: Jing
authors.initials: J
authors.lastname: Lu
authors.forename: Mengyi
authors.initials: M
authors.lastname: Sun
authors.forename: Keqiong
authors.initials: K
authors.lastname: Ye
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites; D018360:Crystallography, X-Ray; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D020125:Mutation, Missense; D009687:Nuclear Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D009690:Nucleic Acid Conformation; D011485:Protein Binding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D012335:RNA, Ribosomal / Q000737:chemistry; D012342:RNA, Small Nuclear / Q000737:chemistry; D012441:Saccharomyces cerevisiae / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D013499:Surface Properties
chemical_list: D009687:Nuclear Proteins; D012335:RNA, Ribosomal; D012342:RNA, Small Nuclear; D029701:Saccharomyces cerevisiae Proteins; C573244:Utp23 protein, S cerevisiae
keywords: 90S pre-ribosome; PIN domain; crystal structure; ribosome synthesis