How do yeast control the expression of their genes? And how is this relevant to beer and wine fermentation? On this page we’ll dive into the details of gene expression regulation, and learn how specific DNA sequences, called promoters, can impact the flavor of fermented beverages.
酵母是如何控制它们基因的表达的?这与啤酒和葡萄酒发酵有什么关系呢?在本页中，我们将深入研究基因表达调控的细节，并了解称为启动子的特定DNA序列如何影响发酵饮料的风味。
What is a promoter? 什么是启动子？
The DNA that makes up every gene can be divided into different functional segments (Figure 1). One segment, called the “coding sequence”, contains the information necessary for producing a protein. A second segment, called the promoter, is located next to the coding sequence and determines precisely when the gene will be expressed, and how many proteins will be produced from it. Essentially, a promoter is responsible for sensing the physiological state of the cell (e.g., nutrient levels, temperature, and pH), and using this information to determine what the appropriate gene expression level should be. Every one of yeast’s approximately 7,000 genes has its own unique promoter, which means that every yeast gene has its own unique level of expression that is specific to that gene’s function.
构成每个基因的DNA可以分成不同的功能片段(图1)。其中一个片段称为“编码序列”，包含产生蛋白质所需的信息。第二个片段被称为启动子，位于编码序列旁边，它精确地决定了基因何时表达，以及它将产生多少蛋白质。从本质上讲，启动子负责感知细胞的生理状态(例如，营养水平、温度和pH值)，并利用这些信息确定适当的基因表达水平。酵母的大约7000个基因中的每一个都有自己独特的启动子，这意味着每个酵母基因都有自己独特的表达水平，这是特定于该基因功能的。
Figure 1.
The ATF1 promoter and coding sequence.
图1 所示ATF1启动子和编码序列
As discussed in our
lesson on gene expression regulation
, the expression level of a gene will change in response to its environment. These expression changes are controlled by the gene’s promoter. For simplicity, scientists often characterize promoters on a sliding scale from strong to weak. Strong promoters are those that, in most environments, drive high levels of gene expression, resulting in many proteins being produced. Conversely, weak promoters are those that generally drive low levels of expression, resulting in few proteins being produced.
正如我们在基因表达调控课程中所讨论的，基因的表达水平会随着环境的变化而改变。这些表达变化是由基因启动子控制的。为了简单起见，科学家们经常将启动子的特征从强到弱进行变化。在大多数环境中，强启动子驱动高水平的基因表达，导致许多蛋白质的产生。相反，弱启动子通常驱动低水平的表达，导致产生很少的蛋白质。
Why are promoters important for beer and winemaking?
为什么启动子对啤酒和葡萄酒酿造很重要?
Many of the differences between various brewing and winemaking strains result from differences in the regulation of gene expression. For example, brewers have long known that Hefeweizen strains produce more isoamyl acetate (banana-like flavor) than other ale strains. Scientists recently discovered that this is because Hefeweizen strains strongly express the ATF1 gene, which encodes an isoamyl acetate biosynthesizing enzyme
¹
. The reason that Hefeweizen strains highly express ATF1 is likely that these strains have mutations in their ATF1 promoter that increases the level of ATF1 expression (Figure 2).
许多不同酿造和酿酒菌株之间的差异是由于基因表达调控的差异引起的
。例如，
酿酒商早就知道Hefeweizen菌株比其他菌株产生更多的醋酸异戊酯(类似香蕉的味道)
。科学家最近发现，
这是因为Hefeweizen菌株强烈表达ATF1基因，该基因编码醋酸异戊酯生物合成酶
¹。
Hefeweizen菌株高表达ATF1的原因可能是这些菌株的ATF1启动子发生突变，增加了ATF1的表达水平
(图2)。
Aside from the production of isoamyl acetate, many other traits that differ among yeast strains result from differences in the regulation of gene expression. Traits like fermentation speed, flocculation, and volatile thiol biotransformation are all affected by mutations in promoter sequences that change the strength and timing of gene expression. These and other discoveries have made it clear that changes in gene expression can have a huge impact on yeast fermentation performance and the flavor of fermented beverages.
除了醋酸异戊酯的生产，许多其他性状在酵母菌株之间的差异是由于基因表达调节的差异
。诸如发酵速度、絮凝和挥发性硫醇生物转化等性状都受到启动子序列突变的影响，这些突变会改变基因表达的强度和时间。这些和其他的发现清楚地表明，
基因表达的变化会对酵母的发酵性能和发酵饮料的风味产生巨大的影响
。
Figure 2.
A strong ATF1 promoter results in beer with banana-like flavors.
图2 强大的ATF1启动子使啤酒具有香蕉般的风味
Researchers at Berkeley Yeast have found that modifying gene expression levels can also be a key strategy in creating yeast strains with enhanced fermentation traits. By making targeted changes to the DNA sequence of a gene’s promoter, we can precisely control the timing and strength of that gene’s expression. This fine degree of genetic control can be incredibly useful in creating strains that produce specific concentrations of flavor molecules. You can learn more about this in our discussion of how we bioengineer strains.
