PRIONS OF YEAST

朊病毒是一种传染性蛋白， 哺乳动物海绵状脑病的研究。我们 发现酿酒酵母可以被感染 有两个朊病毒，两个非染色体遗传因子， 性质是那些预测的感染性蛋白质，而不是一个 核酸复制子或病毒。第一，[URE 3]是一种变异形式 Ure 2 p是染色体URE 2基因的蛋白产物， 在调节氮代谢中起重要作用。第二个，PSI， 是Sup 35 p的改变形式，Sup 35 p是翻译释放的亚基， 染色体SUP 35基因的产物。我们发现 在[URE 3]菌株中，Ure 2 p比[URE 3]菌株对蛋白酶消化的抗性更强。 在野生型菌株中，支持[URE 3]的朊病毒模型。这 蛋白酶抗性并不总是伴随着 氮代谢N-末端65个氨基酸残基 在完全不存在的情况下，Ure 2 p足以传播[URE 3] C-末端氮调节结构域。过表达 是URE 2蛋白而不是URE 2 RNA诱导的， [URE 3]的从头形成。C-末端氮调节 结构域仅在共价连接到 N-末端结构域，显示[URE 3]通过 N-末端朊病毒结构域之间的相互作用。我们有 纯化的Ure 2 p接近同质，并已开始表征 正常形态和朊病毒形态的区别某些 C-末端氮调节结构域内的缺失 Ure 2 p导致100倍增加的频率， [URE 3]朊病毒出现。事实上，两个不重叠的部分中的任何一个 当Ure 2 p过表达时，可以诱导新生的 [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].