title: Transcription of protein-coding genes in trypanosomes by RNA polymerase I.
abstract: In eukaryotes, RNA polymerase (pol) II transcribes the protein-coding genes, whereas RNA pol I transcribes the genes that encode the three RNA species of the ribosome [the ribosomal RNAs (rRNAs)] at the nucleolus. Protozoan parasites of the order Kinetoplastida may represent an exception, because pol I can mediate the expression of exogenously introduced protein-coding genes in these single-cell organisms. A unique molecular mechanism, which leads to pre-mRNA maturation by trans-splicing, facilitates pol I-mediated protein-coding gene expression in trypanosomes. Trans-splicing adds a capped 39-nucleotide mini-exon, or spliced leader transcript, to the 5' end of the main coding exon posttranscriptionally. In other eukaryotes, the addition of a 5' cap, which is essential for mRNA function, occurs exclusively as a result of RNA pol II-mediated transcription. Given the assumption that cap addition represents the limiting factor, trans-splicing may have uncoupled the requirement for RNA pol II-mediated mRNA production. A comparison of the alpha-amanitin sensitivity of transcription in naturally occurring trypanosome protein-coding genes reveals that a unique subset of protein-coding genes-the variant surface glycoprotein (VSG) expression sites and the procyclin or the procyclic acidic repetitive protein (PARP) genes-are transcribed by an RNA polymerase that is resistant to the mushroom toxin alpha-amanitin, a characteristic of transcription by RNA pol I. Promoter analysis and a pharmacological characterization of the RNA polymerase that transcribes these genes have strengthened the proposal that the VSG expression sites and the PARP genes represent naturally occurring protein-coding genes that are transcribed by RNA pol I.
authors.affiliation: Department of Pathology, New York University, New York 10016, USA.
authors.forename: M G
authors.initials: MG
authors.lastname: Lee
authors.forename: L H
authors.initials: LH
authors.lastname: Van der Ploeg
mesh_terms: D000546:Amanitins / Q000235:genetics; D000818:Animals; D005786:Gene Expression Regulation; D008562:Membrane Glycoproteins / Q000235:genetics / Q000378:metabolism; D011401:Promoter Regions, Genetic; D015800:Protozoan Proteins / Q000235:genetics* / Q000378:metabolism*; D012318:RNA Polymerase I / Q000378:metabolism*; D012323:RNA Processing, Post-Transcriptional; D012333:RNA, Messenger / Q000378:metabolism; D012335:RNA, Ribosomal / Q000235:genetics; D014158:Transcription, Genetic; D014345:Trypanosoma / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism*; D014346:Trypanosoma brucei brucei / Q000235:genetics / Q000378:metabolism
chemical_list: D000546:Amanitins; D008562:Membrane Glycoproteins; D015800:Protozoan Proteins; D012333:RNA, Messenger; D012335:RNA, Ribosomal; C053277:procyclic acidic repetitive protein, Trypanosoma; D012318:RNA Polymerase I