RNA Abbau in Trypanosoma brucei

在哺乳动物中，基因表达受到多个层面的控制，包括转录、剪接、mRNA降解和翻译。相反，在引起昏睡病的病原体非洲锥虫中，mRNA水平几乎完全通过选择性降解来调节。寄生虫对这一途径的独特依赖不仅使其成为研究外核糖核酸酶的有趣模型，而且为抗寄生虫化疗提供了潜在的靶点。我们之前已经描述了锥虫外泌体，一个负责3'-5' RNA降解的复合物，两个锥虫5‘-3’外切酶（细胞质XRNA和核XRND），以及两个死基化复合物，CAF1/NOT和PAN2/3。所有这些都是寄生虫生存所必需的。在锥虫中，大多数mRNA的组成性降解依赖于CAF1/NOT和PAN2/PAN3复合物的死基化。CAF1蛋白作为一种deadenylase具有自主活性；在本提案中，我们希望找出CAF1与NOT1和复合体中其他蛋白质的关联如何影响CAF1的活性，并确定各种亚基的功能。高度不稳定的锥虫mrna受到XRNA的不依赖于死基化的攻击，但也有另外两种新的锥虫特异性细胞质5‘-3’外切酶。我们的第二个主要目标是确定这两种蛋白的功能-具有锌指结构域的xrnb和XRNC。

In mammals, gene expression is controlled at multiple levels, including transcription, splicing, mRNA degradation and translation. In contrast, in African trypanosomes, the pathogens that cause sleeping sickness, mRNA levels are regulated almost exclusively via selective degradation. The unique dependence of the parasites on this one pathway not only makes the organisms an interesting model for the study of exoribonucleases, but also provides potential targets for anti-parasitic chemotherapy. We have previously characterised the trypanosome exosome, a complex which is responsible for 3'-5' RNA degradation, two trypanosome 5'-3' exonucleases (cytoplasmic XRNA and nuclear XRND), and two deadenylation complexes, CAF1/NOT and PAN2/3. All of these are essential for parasite survival. In trypanosomes, constitutive mRNA degradation of most mRNAs depends on deadenylation by the CAF1/NOT and PAN2/PAN3 complexes. The CAF1 protein is autonomously active as a deadenylase; in this proposal we wish to find out how the association of CAF1 with NOT1 and other proteins in a complex affects CAF1 activity, and determine the functions of the various subunits. Highly unstable trypanosome mRNAs are subjected to deadenylation-independent attack by XRNA, but there are also two other novel trypanosome-specific cytoplasmic 5'-3' exonucleases. Our second major aim is to determine the functions of these two proteins -XRNB, which has a zinc finger domain, and XRNC.