title: The Xist RNA A-repeat comprises a novel AUCG tetraloop fold and a platform for multimerization.
abstract: X-chromosome inactivation (XCI) in female mammals depends on the noncoding RNA X inactivation specific transcript (Xist). The mechanism of chromosome-wide silencing by Xist is poorly understood. While it is established that the 5' region of Xist RNA, comprising the A-repeats and holding 7.5-8.5 copies of a conserved 26-mer sequence, is essential for Xist-mediated silencing, high-resolution structural information for the A-repeats is not available. Here, we report the three-dimensional solution structure of a 14-mer hairpin in the 5' region of a human A-repeat. This hairpin is remarkably stable and adopts a novel AUCG tetraloop fold, the integrity of which is required for silencing. We show that, contrary to previous predictions, the 3' region of single or tandem A-repeats mediates duplex formation in vitro. Significantly, mutations in this region disrupt the inter-repeat duplex formation in vitro and abrogate the silencing function of Xist A-repeats in vivo. Our data suggest that the complete A-repeat region may be stabilized by inter-repeat duplex formation and, as such, may provide a platform for multimerization and specific recognition of the AUCG tetraloops by trans-acting factors.
authors.affiliation: Institute of Structural Biology, Helmholtz Zentrum München, 85764 Neuherberg, Germany.
authors.forename: Malgorzata M
authors.initials: MM
authors.lastname: Duszczyk
authors.forename: Anton
authors.initials: A
authors.lastname: Wutz
authors.forename: Vladimir
authors.initials: V
authors.lastname: Rybin
authors.forename: Michael
authors.initials: M
authors.lastname: Sattler
mesh_terms: D000818:Animals; D019281:Dimerization; D006801:Humans; D008958:Models, Molecular; D009690:Nucleic Acid Conformation; D059370:RNA Folding; D062085:RNA, Long Noncoding; D022661:RNA, Untranslated / Q000737:chemistry* / Q000378:metabolism; D012091:Repetitive Sequences, Nucleic Acid
chemical_list: D062085:RNA, Long Noncoding; D022661:RNA, Untranslated; C077885:XIST non-coding RNA