Sadeghi N, Rütz M L, Menees T M
School of Biological Sciences, University of Missouri, Kansas City, USA.
Arch Virol. 2001 Oct;146(10):1919-34. doi: 10.1007/s007050170042.
The long terminal repeat (LTR) retrotransposons of the yeast Saccharomyces cerevisiae are similar in their structures and life cycles to animal retroviruses. The yeast LTR retrotransposon Ty3 does not transpose under conditions where the cellular stress response is activated. During stress, mature Ty3 proteins, indicative of the formation of intracellular Ty3 viruslike particles (VLPs), do not accumulate. In order to examine the role of stress proteins in Ty3 transposition, a sensitive genetic assay was developed to measure VLP formation. The assay employs a Ty3 element marked with a mutant allele of the yeast HIS3 gene (his3AI). To create a stable His+ phenotype, Ty3 must form VLPs, reverse transcribe Ty3 RNA into cDNA, and then insert the cDNA into either chromosomal or plasmid DNA. Using this assay, thermal inhibition of Ty3 transposition was evident at temperatures as low as 30 degrees C. The level of production of mature Ty3 proteins parallels the transposition frequency. Although overexpression of the yeast UBP3 gene allows VLPs to form and transposition to occur in the constitutively stressed ssa1 ssa2 strain, it does not alleviate the inhibition of these processes during stress induced by heat or ethanol. This suggests that the genetic and physical modes of stress response induction are not equivalent.
酿酒酵母的长末端重复序列（LTR）逆转座子在结构和生命周期上与动物逆转录病毒相似。酵母LTR逆转座子Ty3在细胞应激反应被激活的条件下不会发生转座。在应激期间，指示细胞内Ty3病毒样颗粒（VLP）形成的成熟Ty3蛋白不会积累。为了研究应激蛋白在Ty3转座中的作用，开发了一种灵敏的遗传检测方法来测量VLP的形成。该检测方法使用一个标记有酵母HIS3基因（his3AI）突变等位基因的Ty3元件。为了产生稳定的His+表型，Ty3必须形成VLP，将Ty3 RNA逆转录成cDNA，然后将cDNA插入染色体或质粒DNA中。使用这种检测方法，在低至30摄氏度的温度下，Ty3转座的热抑制作用就很明显。成熟Ty3蛋白的产生水平与转座频率平行。尽管酵母UBP3基因的过表达能使VLP在持续应激的ssa1 ssa2菌株中形成并发生转座，但在热或乙醇诱导的应激期间，它并不能减轻对这些过程的抑制。这表明应激反应诱导的遗传模式和物理模式并不等同。
