PRIONS OF YEAST

Prion是一种具有感染性的蛋白质，这一概念源于 来自哺乳动物海绵状脑病的研究。我们 发现酵母菌可以感染酿酒酵母 有两个Prion，两个非染色体的遗传元件，它们 属性是预测的具有感染性的蛋白质，而不是 核酸复制子或病毒。第一个，[URE3]是更改后的形式 Ure2p，染色体URE2基因的蛋白质产物 在调节氮代谢方面很重要。第二，[PSI]， 是Sup35P的更改形式，Sup35P是翻译版本的一个子单元 染色体SUP35基因的因子和产物。我们发现 Ure2p在[URE3]菌株中对蛋白酶消化的抵抗力比 在野生型菌株中，支持[URE3]的普恩模型。这 蛋白水解酶抗性不是去阻遏的恒定伴随 氮代谢。其N-端65个氨基酸残基 在完全不存在的情况下，Ure2p足以传播[URE3 C-末端的氮调节结构域。过度表达 是URE2蛋白，而不是URE2 RNA，是诱导 [URE3]的从头形成。C端氮素调节 结构域仅在共价连接到 N-末端结构域，表明[URE3]由 N-末端蛋白结构域之间的相互作用。我们有 纯化的Ure2p接近均一，并已开始表征 正常形式和普里子形式之间的区别。一定的 的C-末端氮调节结构域内的缺失 Ure2p导致100倍的频率增加， [URE3]Prion出现了。事实上，两个不重叠的部分中的任何一个 当Ure2p过度表达时，可以诱导从头开始出现 [URE3]。

A prion is an infectious protein, a concept derived from studies of mammalian spongiform encephalopathies. We discovered that the yeast Saccharomyces cerevisiae can be infected with two prions, two non-chromosomal genetic elements whose properties are those predicted for an infectious protein, not a nucleic acid replicon or a virus. The first, [URE3] is an altered form of Ure2p, the protein product of the chromosomal URE2 gene important in regulation of nitrogen metabolism. The second, [PSI], is an altered form of Sup35p, a subunit of the translation release factor and product of the chromosomal SUP35 gene. We find that Ure2p is more resistant to protease digestion in [URE3] strains than in wild-type strains, supporting the prion model for [URE3]. This protease resistance is not a constant concomitant of derepression of nitrogen metabolism. The N-terminal 65 aminoacid residues of Ure2p is sufficient to propagate [URE3], in the complete absence of the C-terminal nitrogen regulation domain. The overexpression of the URE2 protein, and not the URE2 RNA, is what induces the de novo formation of [URE3]. The C-terminal nitrogen regulation domain is only inactivated when covalently attached to the N-terminal domain, showing that [URE3] is propagated by interactions between the N-terminal prion domains. We have purified Ure2p to near homogeneity and have begun to characterize the difference between the normal and prion forms. Certain deletions within the C-terminal nitrogen regulation domain of Ure2p result in a 100-fold increase the frequency with which the [URE3] prion arises. In fact, either of two non-overlapping parts of Ure2p can, when overexpressed, induce the de novo appearance of [URE3].