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  • The EMBO Journal (2006) 25, 4513 - 4523
  • doi:10.1038/sj.emboj.7601328

Published online: 14 September 2006

  • Subject Category:

Sm core variation in spliceosomal small nuclear ribonucleoproteins from Trypanosoma brucei

Pingping Wang1, Zsofia Palfi1, Christian Preusser1, Stephan Lücke1,a, William S Lane2, Christian Kambach3 and Albrecht Bindereif1

  1. Institut für Biochemie, Justus-Liebig-Universität Giessen, Giessen, Germany
  2. Harvard Microchemistry and Proteomics Analysis Facility, Department of Molecular and Cellular Biology, Harvard University, Cambridge, MA, USA
  3. Structural Biology, Paul Scherrer Institut, Villigen, Switzerland

Correspondence to:

Albrecht Bindereif, Institut für Biochemie, Justus-Liebig-Universität Giessen, Heinrich-Buff-Ring 58, 35392 Giessen, Germany. Tel.: +49 641 99 35 420; Fax: +49 641 99 35 419; E-mail: albrecht.bindereif@chemie.bio.uni-giessen.de

aPresent address: Howard Hughes Medical Institute, Program in Gene Function and Expression, University of Massachusetts Medical School, 364 Plantation Street, Worcester, MA 01605, USA

Received 23 January 2006; Accepted 16 August 2006

Messenger RNA processing in trypanosomes by cis and trans splicing requires spliceosomal small nuclear ribonucleoproteins (snRNPs) U1, U2, U4/U6, and U5, as well as the spliced leader (SL) RNP. As in other eukaryotes, these RNPs share a core structure of seven Sm polypeptides. Here, we report that the identity of the Sm protein constituents varies between spliceosomal snRNPs: specifically, two of the canonical Sm proteins, SmB and SmD3, are replaced in the U2 snRNP by two novel, U2 snRNP-specific Sm proteins, Sm15K and Sm16.5K. We present a model for the variant Sm core in the U2 snRNP, based on tandem affinity purification-tagging and in vitro protein–protein interaction assays. Using in vitro reconstitutions with canonical and U2-specific Sm cores, we show that the exchange of two Sm subunits determines discrimination between individual Sm sites. In sum, we have demonstrated that the heteroheptameric Sm core structure varies between spliceosomal snRNPs, and that modulation of the Sm core composition mediates the recognition of small nuclear RNA-specific Sm sites.

  • Keywords:

    • small nuclear RNA,
    • snRNA,
    • snRNP,
    • splicing,
    • trypanosomes