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Eukaryotic Cell doi:10.1128/EC.00279-07
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

The small trypanosome RNA-binding proteins TbUBP1 and TbUBP2 influence expression of F-box protein mRNAs in bloodstream trypanosomes

Zentrum für Molekulare Biologie der Universität Heidelberg (ZMBH), Im Neuenheimer Feld 282, D-69120 Heidelberg, Germany; Division of Functional Genome Analysis, Deutsches Krebsforschungszentrum, Im Neuenheimer Feld 506, 69120 Heidelberg, Germany; Department of Biochemistry, 80 Tennis Court Rd., Cambridge CB2 1GA, UK; Instituto de Investigaciones Biotecnológicas, Universidad Nacional de General San MartÌn, INTI-Av Gral Paz 5445, Edificio 24,1650 San Martin, Buenos Aires, Argentina

^* To whom correspondence should be addressed. Email: cclayton{at}zmbh.uni-heidelberg.de.

	Abstract

In the African trypanosome Trypanosoma brucei nearly all control of gene expression is post-transcriptional; sequences in the 3'-untranslated regions of mRNAs determine steady-state mRNA levels by regulation of RNA turnover. Here we investigate the roles of two related proteins, TbUBP1 and TbUBP2, containing a single RNA Recognition Motif, in trypanosome gene expression. TbUBP1 and TbUBP2 are in the cytoplasm and nucleus, comprise about 0.1% of the total protein, and are not associated with polysomes or RNA degradation enzymes. Over-expression of TbUBP2 up-regulated the levels of several mRNAs potentially involved in cell division, including the CFB1 mRNA which encodes a protein with a cyclin F-box domain. CFB1 regulation was mediated by the 3'-untranslated region and involved stabilisation of the mRNA. Depletion of TbUBP2 and TbUBP1 inhibited growth and down-regulated expression of the cyclin F box protein gene CFB2; trans splicing was unaffected. Results of pull-down assays indicated that all tested mRNAs were bound to TbUBP2 or TbUBP1, with some preference for CFB1. We suggest that TbUBP1 and TbUBP2 may be relatively non-specific RNA binding proteins, and that specific effects of over-expression or depletion could depend on competition between various different proteins for RNA binding.

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