Regulating regulators to survive nutrient limitation: Lessons from yeast

酿酒酵母在解决真核生物生物学中的基本问题以及在烘焙、饮料和生物乙醇行业中将可发酵糖(如葡萄糖)转化为乙醇和二氧化碳的能力方面，为我们的社会提供了关键的模式生物。虽然酵母更喜欢这种发酵代谢来产生能量，但当葡萄糖耗尽时，它可以有效地利用不可发酵的碳源，如乙醇。在商业上重要的酒精发酵过程中，酵母通常会经历葡萄糖耗尽和乙醇水平增加，这会对酵母的生理和新陈代谢产生负面影响，进而降低发酵效率。我们的首要研究目标是了解酵母对发酵压力的适应机制，并最终利用这些信息开发技术，以提高发酵行业的产能。当葡萄糖充足时，发酵生长所需的基因会被活跃地表达，而那些需要代谢非发酵碳源的基因，如乙醇，则会受到抑制。当葡萄糖耗尽，乙醇是唯一的碳源时，这种转录调控就会逆转。同样，蛋白质的丰度、活性和胞内定位也可以受到可用碳源的调节。尽管已经鉴定和鉴定了几种调控酵母对葡萄糖耗竭适应的调节蛋白和信号机制，但转录适应和目标蛋白周转的详细方面仍然没有解决。我们最近发现了Vid30蛋白复合体(Vid30c)，这是一种E3泛素连接酶，将泛素连接到注定要被破坏的靶蛋白，影响控制发酵代谢的信号机制，影响葡萄糖抑制基因的转录调控，并使己糖转运蛋白能够在葡萄糖耗竭时降解。Vid30c调节这些特定事件的分子机制目前尚不清楚。因此，本研究的目标是确定Vid30c对葡萄糖调节基因表达的影响，并确定和表征其对特定靶蛋白的直接调控以响应碳的供应。我们将结合使用酵母遗传、分子和细胞生物学方法来实现这些目标。Vid30c在转录因子和信号蛋白的表达、丰度、翻译后修饰和亚细胞定位中的作用将为进一步深入了解调控碳供应的调节机制提供基础。这些信息将使人们更好地了解商业发酵，并可能导致开发战略，以提高这种商业上重要的有机体的发酵效率。

Saccharomyces cerevisiae serves our society as a pivotal model organism in resolving fundamental questions in eukaryotic biology, and in its capacity to convert fermentable sugars, such as glucose, into ethanol and CO2 in the baking, beverage and bio-ethanol industries. While yeast prefers this fermentative metabolism to generate energy, it can efficiently use non-fermentable carbon sources, like ethanol, when glucose is depleted. During commercially important alcoholic fermentations, yeast commonly experience glucose depletion and increasing levels of ethanol, which negatively impacts the yeast's physiology and metabolism, which in turn decreases fermentation efficiency. Our overarching research goal is to understand the mechanisms that govern the adaptation of yeast to fermentation stresses, and to ultimately use this information to develop technologies to increase capacity in the fermentation industry. When glucose is abundant, the genes needed for fermentative growth are actively expressed, while those needed to metabolize non-fermentable carbon sources, like ethanol, are inhibited. This transcriptional regulation reverses when glucose is depleted, and ethanol is the sole carbon source. Similarly, the abundance, activity and intracellular localization of proteins can also be regulated by the available carbon source. Despite the identification and characterization of several regulatory proteins and signaling mechanisms that govern the adaptation of yeast to glucose depletion, the detailed aspects of transcriptional adaptation and the turnover of target proteins remain unresolved. We recently showed the Vid30 protein complex (Vid30c), an E3 ubiquitin ligase that links ubiquitin to target proteins destined for destruction, impacts the signaling mechanisms that govern fermentative metabolism, affects the transcriptional regulation of glucose repressed genes, and enables the degradation of the hexose transporters in response to glucose depletion. The molecular mechanisms used by Vid30c to mediate these specific events are currently unknown. Thus, the objectives of the proposed research are to characterize the impact of Vid30c on glucose-regulated gene expression and to identify and characterize its direct regulation of specific target proteins in response to carbon availability. We will use a combination of yeast genetic, molecular and cellular biology approaches to achieve these goals. The role of Vid30c in the expression, abundance, posttranslational modification, and subcellular localization of transcription factors and signaling proteins will provide further fundamental insight into the regulatory mechanisms that govern regulators in response to carbon availability. This information will generate a better understanding of commercial fermentations and could lead to the development of strategies to increase the fermentation efficiency of this commercially important organism.