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Molecular and Cellular Biology, November 2001, p. 7731-7746, Vol. 21, No. 22
Department of Biochemistry and Molecular
Biology, University of Massachusetts, Amherst, Massachusetts
010031; Institut de Genetique
Moleculaire-CNRS, Montpellier Cedex 5, France2;
and Department of Biochemistry, North Carolina State
University, Raleigh, North Carolina 276953
Received 1 May 2001/Returned for modification 31 May 2001/Accepted 13 August 2001
Biogenesis of small nucleolar RNA-protein complexes (snoRNPs)
consists of synthesis of the snoRNA and protein components, snoRNP
assembly, and localization to the nucleolus. Recently, two
nucleoplasmic proteins from mice were observed to bind to a model box
C/D snoRNA in vitro, suggesting that they function at an early stage in
snoRNP biogenesis. Both proteins have been described in other contexts.
The proteins, called p50 and p55 in the snoRNA binding study, are
highly conserved and related to each other. Both have Walker A and B
motifs characteristic of ATP- and GTP-binding and nucleoside
triphosphate-hydrolyzing domains, and the mammalian orthologs
have DNA helicase activity in vitro. Here, we report that the
Saccharomyces cerevisiae ortholog of p50 (Rvb2, Tih2p,
and other names) is required for production of C/D snoRNAs in vivo and,
surprisingly, H/ACA snoRNAs as well. Point mutations in the Walker A
and B motifs cause temperature-sensitive or lethal growth phenotypes
and severe defects in snoRNA accumulation. Notably, depletion of p50
(called Rvb2 in this study) also impairs localization of C/D and
H/ACA core snoRNP proteins Nop1p and Gar1p, suggesting a defect(s) in
snoRNP assembly or trafficking to the nucleolus. Findings from other
studies link Rvb2 orthologs with chromatin remodeling and
transcription. Taken together, the present results indicate that Rvb2
is involved in an early stage of snoRNP biogenesis and may play a role
in coupling snoRNA synthesis with snoRNP assembly and localization.
0270-7306/01/$04.00+0 DOI: 10.1128/MCB.21.22.7731-7746.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
A Well-Connected and Conserved Nucleoplasmic
Helicase Is Required for Production of Box C/D and H/ACA snoRNAs and
Localization of snoRNP Proteins
*
Corresponding author. Mailing address: Department of
Biochemistry and Molecular Biology, Lederle Graduate Research Center, University of Massachusetts, Amherst, MA 01003. Phone: (413) 545-2732. Fax: (413) 545-3291. E-mail: 4nier{at}biochem.umass.edu.
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