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The Box H/ACA snoRNP Assembly Factor Shq1p is a Chaperone Protein Homologous to Hsp90 Cochaperones that Binds to the Cbf5p Enzyme
Authors:Katherine S Godin  Nicolas Leulliot  Herman van Tilbeurgh
Institution:1 Department of Chemistry, University of Washington, Box 351700, Seattle, WA 98195, USA
2 Institut de Biochimie et Biophysique Moléculaire et Cellulaire, Université Paris-Sud 11, 91400 Orsay, France
3 Laboratoire de Cristallographie et RMN Biologiques, Université Paris Descartes, CNRS, 4 Avenue de l'Observatoire, 75006 Paris, France
4 Department of Biochemistry, University of Washington, Box 357350, Seattle, WA 98195, USA
Abstract:Box H/ACA small nucleolar (sno) ribonucleoproteins (RNPs) are responsible for the formation of pseudouridine in a variety of RNAs and are essential for ribosome biogenesis, modification of spliceosomal RNAs, and telomerase stability. A mature snoRNP has been reconstituted in vitro and is composed of a single RNA and four proteins. However, snoRNP biogenesis in vivo requires multiple factors to coordinate a complex and poorly understood assembly and maturation process. Among the factors required for snoRNP biogenesis in yeast is Shq1p, an essential protein necessary for stable expression of box H/ACA snoRNAs. We have found that Shq1p consists of two independent domains that contain casein kinase 1 phosphorylation sites. We also demonstrate that Shq1p binds the pseudourydilating enzyme Cbf5p through the C-terminal domain, in synergy with the N-terminal domain. The NMR solution structure of the N-terminal domain has striking homology to the ‘Chord and Sgt1’ domain of known Hsp90 cochaperones, yet Shq1p does not interact with the yeast Hsp90 homologue in vitro. Surprisingly, Shq1p has stand-alone chaperone activity in vitro. This activity is harbored by the C-terminal domain, but it is increased by the presence of the N-terminal domain. These results provide the first evidence of a specific biochemical activity for Shq1p and a direct link to the H/ACA snoRNP.
Keywords:sno  small nucleolar  RNP  ribonucleoprotein  CS  Chord and Sgt1  CK1  casein kinase 1  HSQC  heteronuclear single quantum coherence  NOE  nuclear Overhauser enhancement  NOESY  NOE spectroscopy  PKA  protein kinase A  CK2  casein kinase 2  BSA  bovine serum albumin  βME  β-mercaptoethanol  TOCSY  total correlated spectroscopy  3D  three-dimensional
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