The Xist RNA A-Repeat Comprises a Novel Aucg Tetraloop Fold and a Platform for Multimerization.
Duszczyk, M.M., Wutz, A., Rybin, V., Sattler, M.(2011) RNA 17: 1973
- PubMed: 21947263 
- DOI: https://doi.org/10.1261/rna.2747411
- Primary Citation of Related Structures:  
2Y95 - PubMed 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.
Organizational Affiliation: 
Institute of Structural Biology, Helmholtz Zentrum München, 85764 Neuherberg, Germany.