Du Zhiqiang, Goncharoff Dustin Kenneth, Cheng Xudong, Li Liming
Department of Biochemistry and Molecular Genetics, the Feinberg School of Medicine, Northwestern University, 320 E Superior St, Searle 7-650, Chicago, IL, 60611, USA.
Mol Microbiol. 2017 Apr;104(1):105-124. doi: 10.1111/mmi.13616. Epub 2017 Jan 26.
The budding yeast, Saccharomyces cerevisiae, harbors several prions that are transmitted as altered, heritable protein conformations. [SWI ] is one such prion whose determinant is Swi1, a subunit of the evolutionarily conserved chromatin-remodeling complex SWI/SNF. Despite the importance of Swi1, the molecular events that lead to [SWI ] prionogenesis remain poorly understood. In this study, we have constructed floccullin-promoter-based URA3 reporters for [SWI ] identification. Using these reporters, we show that the spontaneous formation frequency of [SWI ] is significantly higher than that of [PSI ] (prion form of Sup35). We also show that preexisting [PSI ] or [PIN ] (prion form of Rnq1), or overproduction of Swi1 prion-domain (PrD) can considerably promote Swi1 prionogenesis. Moreover, our data suggest a strain-specific effect of overproduction of Sse1 - a nucleotide exchange factor of the molecular chaperone Hsp70, and its interaction with another molecular chaperone Hsp104 on [SWI ] maintenance. Additionally, we show that Swi1 aggregates are initially ring/ribbon-like then become dot-like in mature [SWI ] cells. In the presence of [PSI ] or [PIN ], Swi1 ring/ribbon-like aggregates predominantly colocalize with the Sup35 or Rnq1 aggregates; without a preexisting prion, however, such colocalizations are rarely seen during Swi1-PrD overproduction-promoted Swi1 prionogenesis. We have thus demonstrated a complex interacting mechanism of yeast prionogenesis.
出芽酵母酿酒酵母含有几种朊病毒，它们以改变的、可遗传的蛋白质构象进行传播。[SWI⁺]就是这样一种朊病毒，其决定因素是Swi1，它是进化上保守的染色质重塑复合物SWI/SNF的一个亚基。尽管Swi1很重要，但导致[SWI⁺]朊病毒形成的分子事件仍知之甚少。在这项研究中，我们构建了基于絮凝蛋白启动子的URA3报告基因用于[SWI⁺]的鉴定。使用这些报告基因，我们表明[SWI⁺]的自发形成频率显著高于[PSI⁺]（Sup35的朊病毒形式）。我们还表明，预先存在的[PSI⁺]或[PIN⁺]（Rnq1的朊病毒形式），或Swi1朊病毒结构域（PrD）的过量表达可显著促进Swi1朊病毒的形成。此外，我们的数据表明分子伴侣Hsp70的核苷酸交换因子Sse1的过量表达及其与另一种分子伴侣Hsp104的相互作用对[SWI⁺]维持具有菌株特异性影响。此外，我们表明Swi1聚集体最初是环状/带状的，然后在成熟的[SWI⁺]细胞中变成点状。在存在[PSI⁺]或[PIN⁺]的情况下，Swi1环状/带状聚集体主要与Sup35或Rnq1聚集体共定位；然而，在没有预先存在的朊病毒的情况下，在Swi1-PrD过量表达促进的Swi1朊病毒形成过程中很少看到这种共定位。因此，我们证明了酵母朊病毒形成的复杂相互作用机制。
