RNA polymerase I transcribes procyclin genes and variant surface glycoprotein gene expression sites in Trypanosoma brucei.
In eukaryotes, RNA polymerase (pol) I exclusively transcribes the large rRNA gene unit (rDNA) and mRNA is synthesized by RNA pol II. The African trypanosome, Trypanosoma brucei, represents an exception to this rule. In this organism, transcription of genes encoding the variant surface glycoprotein (VSG) and the procyclins is resistant to alpha-amanitin, indicating that it is mediated by RNA pol I, while other protein-coding genes are transcribed by RNA pol II. To obtain firm proof for this concept, we generated a T. brucei cell line which exclusively expresses protein C epitope-tagged RNA pol I. Using an anti-protein C immunoaffinity matrix, we specifically depleted RNA pol I from transcriptionally active cell extracts. The depletion of RNA pol I impaired in vitro transcription initiated at the rDNA promoter, the GPEET procyclin gene promoter, and a VSG gene expression site promoter but did not affect transcription from the spliced leader (SL) RNA gene promoter. Fittingly, induction of RNA interference against the RNA pol I largest subunit in insect-form trypanosomes significantly reduced the relative transcriptional efficiency of rDNA, procyclin genes, and VSG expression sites in vivo whereas that of SL RNA, alphabeta-tubulin, and heat shock protein 70 genes was not affected. Our studies unequivocally show that T. brucei harbors a multifunctional RNA pol I which, in addition to transcribing rDNA, transcribes procyclin genes and VSG gene expression sites.
Günzl
Arthur
A
Medizinisch-Naturwissenschaftliches Forschungsinstitut der Universität Tübingen, 72074 Tübingen, Germany.
Bruderer
Thomas
T
Laufer
Gabriele
G
Schimanski
Bernd
B
Tu
Lan-Chun
LC
Chung
Hui-Min
HM
Lee
Pei-Tseng
PT
Lee
Mary Gwo-Shu
MG
D000818:Animals; D004275:DNA, Ribosomal / Q000235:genetics; D015870:Gene Expression; D005786:Gene Expression Regulation; D017125:Genes, Protozoan; D008562:Membrane Glycoproteins / Q000235:genetics* / Q000378:metabolism; D011401:Promoter Regions, Genetic; D015800:Protozoan Proteins / Q000235:genetics / Q000378:metabolism; D012318:RNA Polymerase I / Q000378:metabolism*; D016053:RNA, Protozoan / Q000378:metabolism; D014158:Transcription, Genetic; D014346:Trypanosoma brucei brucei / Q000235:genetics* / Q000378:metabolism; D014643:Variant Surface Glycoproteins, Trypanosoma / Q000235:genetics / Q000378:metabolism*
D004275:DNA, Ribosomal; C406751:GPEET protein, Trypanosoma brucei; D008562:Membrane Glycoproteins; D015800:Protozoan Proteins; D016053:RNA, Protozoan; D014643:Variant Surface Glycoproteins, Trypanosoma; C053277:procyclic acidic repetitive protein, Trypanosoma; D012318:RNA Polymerase I