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Eukaryotic Cell, October 2007, p. 1865-1875, Vol. 6, No. 10
1535-9778/07/$08.00+0 doi:10.1128/EC.00134-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Yaron Vagima,1,
Hanoch Goldshmidt,1,
Avigail Erlanger,1
Vered Ozeri,1
James Vince,2
Malcolm J. McConville,2
Dennis M. Dwyer,3
Scott M. Landfear,4 and
Shulamit Michaeli1*
The Mina and Everard Goodman Faculty of Life Science, Bar Ilan University, Ramat-Gan 52900, Israel,1 Department of Biochemistry and Molecular Biology, University of Melbourne, Bio21 Molecular Sciences and Biotechnology Institute, Parkville, Victoria, Australia,2 Cell Biology Section, Laboratory of Parasitic Diseases, NIAID, National Institutes of Health, Bethesda, Maryland,3 Department of Molecular Microbiology and Immunology, Oregon Health and Science University, Portland, Oregon 972394
Received 23 April 2007/ Accepted 23 July 2007
Protein translocation across the endoplasmic reticulum is mediated by the signal recognition particle (SRP). In this study, the SRP pathway in trypanosomatids was down-regulated by two approaches: RNA interference (RNAi) silencing of genes encoding SRP proteins in Trypanosoma brucei and overexpression of dominant-negative mutants of 7SL RNA in Leptomonas collosoma. The biogenesis of both signal peptide-containing proteins and polytopic membrane proteins was examined using endogenous and green fluorescent protein-fused proteins. RNAi silencing of SRP54 or SRP68 in T. brucei resulted in reduced levels of polytopic membrane proteins, but no effect on the level of signal peptide-containing proteins was observed. When SRP deficiency was achieved in L. collosoma by overexpression of dominant-negative mutated 7SL RNA, a major effect was observed on polytopic membrane proteins but not on signal peptide-containing proteins. This study included two trypanosomatid species, tested various protein substrates, and induced depletion of the SRP pathway by affecting either the levels of SRP binding proteins or that of SRP RNA. Our results demonstrate that, as in bacteria but in contrast to mammalian cells, the trypanosome SRP is mostly essential for the biogenesis of membrane proteins.
Published ahead of print on 22 August 2007.
Y.L., Y.V., and H.G. contributed equally to this study.
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