EC Accepts, published online ahead of print on 19 June 2009

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Eukaryotic Cell doi:10.1128/EC.00090-09
Copyright (c) 2009, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Special Sm core complex functions in assembly of the U2 small nuclear ribonucleoprotein of Trypanosoma brucei

Christian Preußer, Zsofia Palfi, and Albrecht Bindereif^*

Institute of Biochemistry, Justus Liebig University of Giessen, D-35392 Giessen, Germany

^* To whom correspondence should be addressed. Email: albrecht.bindereif{at}chemie.bio.uni-giessen.de.

Processing of polycistronic pre-mRNAs in trypanosomes requires spliceosomal small ribonucleoprotein complexes (snRNPs) U1, U2, U4/U6, U5, and SL, each of which contains a core of seven Sm proteins. Recently we reported first evidence for a core variation in spliceosomal snRNPs; specifically, in the trypanosome U2 snRNP two of the canonical Sm proteins, SmB and SmD3, are replaced by two U2-specific Sm proteins, Sm15K and Sm16.5K. Here we identify the U2-specific, nuclear-localized U2B'' protein from Trypanosoma brucei. U2B'' interacts with a second U2 snRNP protein, U2-40K (U2A'), which in turn contacts the U2-specific Sm16.5K/15K subcomplex. Together they form a high-affinity, U2-specific binding complex. This trypanosome-specific assembly differs from the mammalian system and provides a functional role of the Sm core variation found in the trypanosomal U2 snRNP.

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