Alpha-amanitin-insensitive transcription of variant surface glycoprotein genes provides further evidence for discontinuous transcription in trypanosomes.
Alpha-amanitin-insensitive transcription of variant surface glycoprotein genes provides further evidence for discontinuous transcription in trypanosomes.
复制标题
变异表面糖蛋白基因的α-鹅膏蕈碱不敏感转录为锥虫中的不连续转录提供了进一步的证据。
作者：
J. Kooter;P. Borst
布鲁氏锥虫中的许多(如果不是全部)mRNAs以相同的35个核苷酸序列开始，分别编码在聚集的所谓微型外显子重复序列中。从这些微小外显子重复141个核苷酸的前体RNA，在其5‘端转录35个核苷酸序列。间接证据表明，这种RNA在第二步与前mRNA转录本有关。我们在分离的锥虫细胞核中研究了RNA合成对α-Amanitin的敏感性。每毫升5微克的α-Amanitin几乎完全抑制几个蛋白质编码基因的转录，而每毫升200微克的α-Amanitin对微小外显子的转录有强烈的抑制作用。相反，每毫升1000微克的α-Amanitin不能抑制变异表面糖蛋白(VSG)基因的转录，主要rRNAs的基因转录也不受抑制。由于成熟的VSG mRNAs始于35-NT序列，我们的结果提供了额外的证据，证明35-NT序列和VSG mRNA的主要部分来自独立的转录单位，它们由(部分)不同的RNA聚合酶转录。
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.