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      Assembly and trafficking of box C/D and H/ACA snoRNPs

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          Box C/D and box H/ACA snoRNAs are abundant non-coding RNAs that localize in the nucleolus and mostly function as guides for nucleotide modifications. While a large pool of snoRNAs modifies rRNAs, an increasing number of snoRNAs could also potentially target mRNAs. ScaRNAs belong to a family of specific RNAs that localize in Cajal bodies and that are structurally similar to snoRNAs. Most scaRNAs are involved in snRNA modification, while telomerase RNA, which contains H/ACA motifs, functions in telomeric DNA synthesis. In this review, we describe how box C/D and H/ACA snoRNAs are processed and assembled with core proteins to form functional RNP particles. Their biogenesis involve several transport factors that first direct pre-snoRNPs to Cajal bodies, where some processing steps are believed to take place, and then to nucleoli. Assembly of core proteins involves the HSP90/R2TP chaperone-cochaperone system for both box C/D and H/ACA RNAs, but also several factors specific for each family. These assembly factors chaperone unassembled core proteins, regulate the formation and disassembly of pre-snoRNP intermediates, and control the activity of immature particles. The AAA+ ATPase RUVBL1 and RUVBL2 belong to the R2TP co-chaperones and play essential roles in snoRNP biogenesis, as well as in the formation of other macro-molecular complexes. Despite intensive research, their mechanisms of action are still incompletely understood.

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          Most cited references 155

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          Non-coding RNAs: lessons from the small nuclear and small nucleolar RNAs.

          Recent advances have fuelled rapid growth in our appreciation of the tremendous number, diversity and biological importance of non-coding (nc)RNAs. Because ncRNAs typically function as ribonucleoprotein (RNP) complexes and not as naked RNAs, understanding their biogenesis is crucial to comprehending their regulation and function. The small nuclear and small nucleolar RNPs are two well studied classes of ncRNPs with elaborate assembly and trafficking pathways that provide paradigms for understanding the biogenesis of other ncRNPs.
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            Chaperone machines for protein folding, unfolding and disaggregation.

            Molecular chaperones are diverse families of multidomain proteins that have evolved to assist nascent proteins to reach their native fold, protect subunits from heat shock during the assembly of complexes, prevent protein aggregation or mediate targeted unfolding and disassembly. Their increased expression in response to stress is a key factor in the health of the cell and longevity of an organism. Unlike enzymes with their precise and finely tuned active sites, chaperones are heavy-duty molecular machines that operate on a wide range of substrates. The structural basis of their mechanism of action is being unravelled (in particular for the heat shock proteins HSP60, HSP70, HSP90 and HSP100) and typically involves massive displacements of 20-30 kDa domains over distances of 20-50 Å and rotations of up to 100°.
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              The snoRNA HBII-52 regulates alternative splicing of the serotonin receptor 2C.

              The Prader-Willi syndrome is a congenital disease that is caused by the loss of paternal gene expression from a maternally imprinted region on chromosome 15. This region contains a small nucleolar RNA (snoRNA), HBII-52, that exhibits sequence complementarity to the alternatively spliced exon Vb of the serotonin receptor 5-HT(2C)R. We found that HBII-52 regulates alternative splicing of 5-HT(2C)R by binding to a silencing element in exon Vb. Prader-Willi syndrome patients do not express HBII-52. They have different 5-HT(2C)R messenger RNA (mRNA) isoforms than healthy individuals. Our results show that a snoRNA regulates the processing of an mRNA expressed from a gene located on a different chromosome, and the results indicate that a defect in pre-mRNA processing contributes to the Prader-Willi syndrome.

                Author and article information

                RNA Biol
                RNA Biol
                RNA Biology
                Taylor & Francis
                7 October 2016
                7 October 2016
                : 14
                : 6 , Cajal Bodies Guest Editor: Karla M. Neugebauer
                : 680-692
                [a ]Ingénierie Moléculaire et Physiopathologie Articulaire, UMR 7365 CNRS , 9 Avenue de la forêt de Haye, 54505 Vandoeuvre-les-Nancy Cedex, France, Université de Lorraine, Campus Biologie –Santé , CS 50184, 54505 Vandoeuvre-les-Nancy Cedex, France
                [b ]Institut de Génétique Moléculaire de Montpellier, UMR 5535 CNRS , 1919 route de Mende, 34293 Montpellier cedex 5, France, Université de Montpellier , 163 rue Auguste Broussonnet, 34090 Montpellier, France
                Author notes
                © 2017 The Author(s). Published with license by Taylor & Francis Group, LLC

                This is an Open Access article distributed under the terms of the Creative Commons Attribution-Non-Commercial License (, which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. The moral rights of the named author(s) have been asserted.

                Page count
                Figures: 3, Tables: 1, References: 155, Pages: 13

                Molecular biology

                scarna, box c/d rnp, box h/aca rnp, hsp90/r2tp, rnp assembly, rnp trafficking, snorna


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