Eukaryotic Cell doi:10.1128/EC.00411-06
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.
SL RNA gene transcription in Trypanosoma brucei requires transcription factor TFIIH
Ju Huck Lee,
Tu N Nguyen,
Bernd Schimanski,
and
Arthur Günzl*
Department of Genetics and Developmental Biology, Department of Molecular, Microbial and Structural Biology, University of Connecticut Health Center, 263 Farmington Avenue, Farmington, CT 06030-3301, USA
* To whom correspondence should be addressed. Email:
gunzl{at}uchc.edu.
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Abstract |
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Trypanosomatid parasites share a gene expression mode which differs greatly from that of their human and insect hosts. In these unicellular eukaryotes, protein coding genes are transcribed polycistronically and individual mRNAs are processed from precursors by spliced leader (SL) trans splicing and polyadenylation. In trans splicing, the SL RNA is consumed through a transfer of its 5'-terminal part to the 5'-end of mRNAs. Since all mRNAs are trans spliced, the parasites depend on strong and continuous SL RNA synthesis mediated by RNA polymerase II. As essential factors for SLRNA transcription in T. brucei, the general transcription factor (GTF) IIB and a complex, consisting of the TBP-related protein 4, the small nuclear RNA-activating protein complex, and TFIIA, were recently identified. Although T. brucei TFIIA and TFIIB are extremely divergent to their counterparts in other eukaryotes, their characterization suggested that trypanosomatids do form a class II transcription pre-initiation complex (PIC) at the SLRNA promoter and harbor orthologues of other known GTFs. TFIIH is a GTF which functions in transcription initiation, DNA repair and cell cycle control. Here, we investigated whether a T. brucei TFIIH is important for SLRNA transcription and found that silencing the expression of the highly conserved TFIIH subunit XPD in T. brucei affected SLRNA synthesis in vivo and depletion of this protein from extract abolished SLRNA transcription in vitro. Since we also identified orthologues of the TFIIH subunits XPB, p52/TFB2 and p44/SSL1 co-purifying with TbXPD, we concluded that the parasite harbors a TFIIH which is indispensable for SLRNA transcription.
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