Talk abstracts

Talk on Saturday 01:30-01:50pm submitted by Alexander Jamieson

Small angle x-ray scattering analysis of the basepaired complex of U6 and U2 snRNAs points to an RNA chaperone role for proteins in assembly of the spliceosomal active site

Zheng Li, Shihu Wang, Elena Dormidontova (Department of Macromolecular Science & Engineering, Case Western Reserve University), Farshad Niazi, Caroline Lee, Saba Valadkhan (Center for RNA Molecular Biology, School of Medicine, Case Western Reserve University), Alex. M. Jamieson (Department of Macromolecular Science & Engineering, Case Western Reserve University), James L. Manley (Department of Biological Sciences, Columbia University)

Abstract:
U6 and U2 spliceosomal small nuclear RNAs (snRNAs) play central roles in splicing, an ubiquitous and essential step in eukaryotic gene expression. In activated spliceosomes these two snRNAs form a functionally-critical basepaired complex and evidence indicates that in vitro-assembled complexes of these two snRNAs can perform an in vitro splicing reaction9[1]. However, despite its functional importance, structural information on the U6/U2 basepaired complex has been lacking. Here we describe small-angle X-Ray scattering (SAXS) structural analyses of an in vitro-assembled, base-paired complex formed by central domains of human U6 and U2 snRNAs. The results indicate the snRNAs fold into a four-way junction-like structure [2], in which the intramolecular stemloop of U6 and the ACAGAGA-containing stem are co-axially stacked, with the ISL and helix II showing side-by-side stacking. Our data suggests that the spontaneous folding of the snRNAs is modified by spliceosomal proteins, which help juxtapose functionally-critical residues, and thus indicates a RNA chaperone role for proteins in the spliceosomal active site.

References:
[1] Valadkhan, S.; Mohammadi, A.; Jaladat, Y.; Geisler, S., 2009, Protein-free small nuclear RNAs catalyze a two-step splicing reaction, Proc. Natl Acad Sci USA, 106(29), 11901-11906.
[2] Lilley, D. M. J., Quart. Rev. Biophys. 2000. 33, 109-159.

Keywords: model spliceosome, Synchrotron SAXS, four-way junction