MECHANISM OF ANTIGENIC VARIATION IN TRYPANOSOMA BRUCEI

锥虫的抗原性变异是由周期性 细胞表面糖蛋白变异体编码基因的表达 (VSG)涂层。免疫功能不同的表面涂层的表达 使转换为新外套表达的锥体得以逃脱 免疫破坏。抗原变异背后的遗传程序 涉及不同VSG基因的或多或少的有序表达。一些人 VSG基因可以通过基因的复制转座激活 位于染色体末端或端粒的表达部位；其他VSG基因 总是位于端粒的基因可以在不被检测到的情况下被激活 基因附近的基因组重组。我已经证明了 其中有几个代表了不同的端粒表达位点 不同的染色体(4)。这个项目的目的是调查 这些端粒表达位点的相互排斥激活和 染色体重组在其调控中的作用。 最近，我已经能够通过一种方法来确定锥虫染色体的大小 新的电泳法。这允许检测到以前的 未被观察到的染色体重排，取代了数百个 千基波。这些可以解释转录调控的原因。 VSG基因启动子的位置效应对表达部位的影响 染色体重组。为了考察相互排斥的 表达位点I的调节将分离重组突变体， 克隆包含VSG基因1.8表达位点的150kb区域 探讨重组对血管紧张素转换酶基因的调控作用 血管紧张素转换酶基因启动子在大肠杆菌中的表达 激活相同位点的不同重组突变体。我也会 检查染色体的频率和机制 重组：通过克隆突变的染色体重组区 以及通过确定 供体和受体部位的核苷酸序列。我会比较一下 布鲁氏毛滴虫的染色体谱系和染色体稳定性 其他动原体纲(锥虫属种，利什曼原虫， Leptomonas和Herpetomonas)。这将使我们对染色体有更深入的了解 这些原生动物的稳定性和突变频率是很重要的 对于我们对塑造寄生虫基因组的力量的理解 不断适应高度多变的环境。

Antigenic variation of trypanosomes is brought about by the periodic expression of genes that code for the Variant Cell Surface Glycoprotein (VSG) coat. The expression of immunologically distinct surface coats enables trypanosomes that switched to the expression of new coat to escape immune destruction. The genetic program underlying antigenic variation involves the more or less ordered expression of different VSG genes. Some VSG genes can be activated by a duplicative transposition of the gene to an expression site located at a chromosome end or telomere; other VSG genes that are always located at telomeres can be activated without detectable genomic recombinations in the vicinity of the gene. I have shown that several of these represent different telomeric expression sites situated on different chromosomes (4). It is the aim of this project to investigate the mutually exclusive activation of these telomeric expression sites and the involvement of chromosomal recombinations in their regulation. Recently I have been able to size separate trypanosomal chromosomes by a new electrophoretic technique. This allowed the detection of previously unobserved chromosome rearrangements, displacing hundreds of kilobasepairs. These could explain transcriptional regulation of the expression sites by a position effect on the VSG gene promoter due to the chromosomal recombinations. In order to examine the mutually exclusive regulation of the expression sites I will isolate recombination mutants, clone an area of 150 kb comprising the expression site of VSG gene 1.8 and investigate the regulatory effect of the recombinations on VSG gene expression: by localisation and comparison of the VSG gene promoter in different recombination mutants that activated the same site. I will also examine the frequency and mechanism underlying the chromosome recombinations: by cloning of the mutant chromosome recombination regions and analysis of the nature of the recombinations by determination of the nucleotide sequences at donor and acceptor sites. I will compare the chromosome repertoire and chromosomal stability in T.brucei, with that of other Kinetoplastida (species of the genera Trypanosoma, Leishmania, Leptomonas, and Herpetomonas). This will give insight in the chromosome stability and mutation frequency in these protozoa which is of importance for our understanding of the forces molding the parasites genome in its continuous adaptation to a highly variable environment.