Pays E
Department of Molecular Biology, Free University of Brussels, Rhode St Genèse, Belgium.
Res Microbiol. 1991 Jul-Aug;142(6):731-5. doi: 10.1016/0923-2508(91)90088-r.
The major surface antigens of Trypanosoma brucei are the VSG (variant surface glycoprotein) at the bloodstream stage, and procyclin at the procyclic stage. Variation in the VSG allows the parasite to escape the antibody response of its mammalian host. This occurs through either DNA rearrangement in the telomeric VSG gene expression site, or alternate activation, without DNA rearrangement, of different telomeric expression sites. The VSG and procyclin genes each belong to large, polycistronic transcription units. Although the promoters of these units are both active at the two main stages of the parasite life cycle, stage-specific controls operating at the level of RNA elongation and processing lead to strictly differential expression of the end products of the two units. Despite their mutually exclusive control of expression, the VSG and procyclin transcription units share common characteristics. Both contain a similar gene, and both are transcribed by the same type of RNA polymerase, unusually resistant to alpha-amanitin. Among the eight genes present in the VSG transcription unit, two may be involved in the synthesis of cyclic AMP. The function of the other genes is unknown.
布氏锥虫的主要表面抗原在血流阶段是变异表面糖蛋白（VSG），在前循环阶段是前环素。VSG的变异使寄生虫能够逃避其哺乳动物宿主的抗体反应。这通过端粒VSG基因表达位点的DNA重排，或不同端粒表达位点在无DNA重排情况下的交替激活来实现。VSG基因和前环素基因各自属于大型多顺反子转录单元。尽管这些单元的启动子在寄生虫生命周期的两个主要阶段均有活性，但在RNA延伸和加工水平上起作用的阶段特异性调控导致这两个单元的终产物严格差异表达。尽管VSG和前环素转录单元对表达的控制相互排斥，但它们具有共同特征。两者都包含一个相似的基因，并且都由同一种对α-鹅膏蕈碱异常抗性的RNA聚合酶转录。在VSG转录单元中的八个基因中，有两个可能参与环磷酸腺苷的合成。其他基因的功能尚不清楚。
