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J. Biol. Chem., Vol. 279, Issue 18, 18210-18219, April 30, 2004

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Identification and Functional Characterization of Lsm Proteins in Trypanosoma brucei^*

Qing Liu, Xue-hai Liang, Shai Uliel, Myriam Belahcen, Ron Unger, and Shulamit Michaeli

From the Faculty of Life Sciences, Bar-Ilan University, Ramat-Gan 52900, Israel

RNA interference of Sm proteins in Trypanosoma brucei demonstrated that the stability of the small nuclear RNAs (U1, U2, U4, U5) and the spliced leader RNA, but not U6 RNA, were affected upon Sm depletion (Mandelboim, M., Barth, S., Biton, M., Liang, X. H., and Michaeli, S. (2003) J. Biol. Chem. 278, 51469–51478), suggesting that Lsm proteins that bind and stabilize U6 RNA in other eukaryotes should exist in trypanosomes. In this study, we identified seven Lsm proteins (Lsm2p to Lsm8p) and examined the function of Lsm3p and Lsm8p by RNA interference silencing. Both Lsm proteins were found to be essential for U6 stability and mRNA decay. Silencing was lethal, and cis- and trans-splicing were inhibited. Importantly, silencing also affected the level of U4.U6 and the U4.U6/U5 tri-small nuclear ribonucleoprotein complexes. The presence of Lsm proteins in trypanosomes that diverged early in the eukaryotic lineage suggests that these proteins are highly conserved in both structure and function among eukaryotes. Interestingly, however, Lsm1p that is specific to the mRNA decay complex was not identified in the genome data base of any kinetoplastidae, and the Lsm8p that in other eukaryotes exclusively functions in U6 stability was found to function in trypanosomes also in mRNA decay. These data therefore suggest that in trypanosomes only a single Lsm complex may exist.

Received for publication, January 21, 2004 , and in revised form, February 23, 2004.

^* This work was supported by a grant from the Israeli German Foundation. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

Contributed equally to this study.

Howard Hughes International Scholar in Molecular Parasitology. To whom correspondence should be addressed. Tel.: 972-3-5318068; Fax: 972-3-5351824; E-mail: michaes{at}mail.biu.ac.il.

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