title: Processing of intron-encoded box C/D small nucleolar RNAs lacking a 5',3'-terminal stem structure.
abstract: The C and D box-containing (box C/D) small nucleolar RNAs (snoRNAs) function in the nucleolytic processing and 2'-O-methylation of precursor rRNA. In vertebrates, most box C/D snoRNAs are processed from debranched pre-mRNA introns by exonucleolytic activities. Elements directing accurate snoRNA excision are located within the snoRNA itself; they comprise the conserved C and D boxes and an adjoining 5',3'-terminal stem. Although the terminal stem has been demonstrated to be essential for snoRNA accumulation, many snoRNAs lack a terminal helix. To identify the cis-acting elements supporting the accumulation of intron-encoded box C/D snoRNAs devoid of a terminal stem, we have investigated the in vivo processing of the human U46 snoRNA and an artificial snoRNA from the human beta-globin pre-mRNA. We demonstrate that internal and/or external stem structures located within the snoRNA or in the intronic flanking sequences support the accumulation of mammalian box C/D snoRNAs lacking a canonical terminal stem. In the intronic precursor RNA, transiently formed external and/or stable internal base-pairing interactions fold the C and D boxes together and therefore facilitate the binding of snoRNP proteins. Since the external intronic stems are degraded during snoRNA processing, we propose that the C and D boxes alone can provide metabolic stability for the mature snoRNA.
authors.affiliation: Laboratoire de Biologie Moléculaire Eucaryote du CNRS, 31062 Toulouse, France.
authors.forename: X
authors.initials: X
authors.lastname: Darzacq
authors.forename: T
authors.initials: T
authors.lastname: Kiss
mesh_terms: D000818:Animals; D002466:Cell Nucleolus / Q000235:genetics*; D006801:Humans; D007438:Introns; D008322:Mammals; D009690:Nucleic Acid Conformation; D012323:RNA Processing, Post-Transcriptional; D020537:RNA, Small Nucleolar / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*
chemical_list: D020537:RNA, Small Nucleolar