YEAST RNA VIROLOGY

我们已经描述了两种dsRNA病毒（L-A和L-BC）和两种ssRNA病毒（L-B和L-C）。 复制子（20S RNA和23S RNA）。 M dsRNA是L-A的一个卫星，编码杀手毒素。 我们发现 7个染色体基因，SKI 1，2，3，4，6，7和8，通过它们的能力， 防止这些复制子对酵母细胞造成致病性。 这四种RNA复制子都产生无帽mRNA，并且缺乏3 'poly（A） 结构 SKI1是一种特异于未加帽mRNA的核糖核酸外切酶， 而我们发现SKI2、SKI3和SKI8基因产物阻断了 非poly（A）mRNA的翻译。 我们发现20个基因的突变 导致M dsRNA缺失的染色体基因在60S 核糖体亚单位 这些突变被ski突变抑制 而不恢复60S亚基缺陷。 我们提出 SKI2、SKI3和SKI8通过以下作用阻断非poly（A）mRNA的翻译： 核糖体生物合成影响60S亚基与 mRNA的3 'poly（A）结构。 我们现在已经克隆了SKI6， SKI7基因。 Ski6p与RNase PH具有同源性，RNase PH是一种去除RNA的酶。 在磷酸解反应中来自tRNA前体的3 '核苷酸（如 多核苷酸磷酸化酶）。 Ski6 - 2突变体对 潮霉素，表明Ski6p参与翻译。 这些 ski6 - 2菌株翻译非poly（A）mRNA比同基因野生型菌株好10倍 类型细胞。 它们还积累了一个38S粒子， 降解的25S rRNA，为60S亚基的改变提供了直接证据 作为非poly（A）mRNA去抑制翻译的原因。 Ski7p 与翻译因子EF 1 α高度同源。 SKI7突变体 对于非poly（A）mRNA的翻译和过表达是去抑制的 Ski7p的缺失导致M dsRNA的缺失。

We have described two dsRNA viruses (L-A and L-BC) and two ssRNA replicons (20S RNA and 23S RNA) in the yeast Saccharomyces cerevisiae. M dsRNA is a satellite of L-A encoding the killer toxin. We discovered 7 chromosomal genes, SKI1, 2, 3, 4, 6, 7, and 8, by their ability to prevent these replicons from causing pathogenicity to yeast cells. These four RNA replicons all make uncapped mRNAs and lack a 3' poly(A) structure. SKI1 is an exoribonuclease specific for uncapped mRNAs, while we showed that the SKI2, SKI3 and SKI8 gene products block the translation of non-poly(A) mRNAs. We showed that mutations in 20 chromosomal genes resulting in loss of M dsRNA are deficient in 60S ribosomal subunits. These mutations are suppressed by ski mutations without restoration of the 60S subunit deficiency. We proposed that SKI2, SKI3 and SKI8 block translation of non-poly(A) mRNA by an effect on ribosome biogenesis affecting the interaction of 60S subunits with the 3' poly(A) structure of the mRNA. We have now cloned the SKI6 and SKI7 genes. Ski6p has homology with RNase PH, an enzyme that removes 3' nucleotides from tRNA precursors in a phosphorolytic reaction (like polynucleotide phosphorylase). Ski6-2 mutants are hypersensitive to hygromycin, an indication of involvement of Ski6p in translation. These ski6-2 strains translate non-poly(A) mRNAs 10x better than isogenic wild type cells. They also accumulate a 38S particle with a partially degraded 25S rRNA, providing direct evidence for altered 60S subunits as the cause of the derepressed translation of non-poly(A) mRNAs. Ski7p is highly homologous to translation factor EF1alpha. The ski7 mutants are derepressed for translation of non-poly(A) mRNAs and overexpression of Ski7p results in loss of M dsRNA.