title: Alpha-amanitin-insensitive transcription of variant surface glycoprotein genes provides further evidence for discontinuous transcription in trypanosomes.
abstract: Many, if not all, mRNAs in T.brucei start with the same sequence of 35 nucleotides, separately encoded in clustered so-called mini-exon repeats. From these mini-exon repeats a 141-nt precursor RNA with the 35-nt sequence at its 5' end is transcribed. Indirect evidence suggests that this RNA is linked in a second step to pre-mRNA transcripts. We have studied the sensitivity of RNA synthesis to alpha-amanitin in isolated trypanosome nuclei. Transcription of several protein coding genes is almost completely inhibited by a concentration of 5 micrograms alpha-amanitin per ml, whereas strong inhibition of mini-exon transcription is achieved with 200 micrograms alpha-amanitin per ml. In contrast, transcription of genes for variant surface glycoproteins (VSGs) is not inhibited by 1000 micrograms alpha-amanitin per ml, as is transcription of the genes for the major rRNAs. Since the mature VSG mRNAs start with the 35-nt sequence, our results provide additional evidence that the 35-nt sequence and the main part of VSG mRNA are produced from independent transcription units, these are transcribed by (partly) different RNA polymerases.
mesh_terms: D000546:Amanitins / Q000494:pharmacology*; D000818:Animals; D002467:Cell Nucleus / Q000502:physiology; D012321:DNA-Directed RNA Polymerases / Q000037:antagonists & inhibitors; D006023:Glycoproteins / Q000235:genetics*; D012319:RNA Polymerase II / Q000378:metabolism; D012320:RNA Polymerase III / Q000378:metabolism; D014158:Transcription, Genetic / Q000187:drug effects; D014346:Trypanosoma brucei brucei / Q000235:genetics*; D014643:Variant Surface Glycoproteins, Trypanosoma
chemical_list: D000546:Amanitins; D006023:Glycoproteins; D014643:Variant Surface Glycoproteins, Trypanosoma; D012319:RNA Polymerase II; D012321:DNA-Directed RNA Polymerases; D012320:RNA Polymerase III