Russell D W, Smith M, Cox D, Williamson V M, Young E T
Nature. 1983;304(5927):652-4. doi: 10.1038/304652a0.
The yeast Saccharomyces cerevisiae has three genetic loci encoding different alcohol dehydrogenase (ADH) isozymes: ADC1, which encodes the classical fermentative isozyme ADHI; ADR2, which encodes the glucose-repressed isozyme ADHII; and ADM, which encodes an ADH isozyme found associated with mitochondria. When yeast are grown on glucose, the ADC1 gene is expressed, and the ADR2 gene repressed. Conversely, growth on a non-fermentable carbon source such as ethanol or glycerol results in derepression of ADR2, and repression of ADC1. The ADC1 and ADR2 genes have been cloned and sequenced, and a number of cis-acting mutations identified that cause constitutive expression of ADR2, and seem to fall into two classes. The most abundant class consists of mutants that cannot be fully derepressed, and do not revert to wild type at a detectable level: these are caused by the insertion of a transposable element into the 5'-flanking region of the gene. The second class of mutants do revert to a glucose-repressed phenotype at a detectable frequency, and when grown on non-fermentable carbon sources derepress ADR2 to levels up to five times those found in wild-type cells. We report here the sequencing of the 5'-flanking regions of two such promoter-up, constitutive ADR2 mutants, in both of which the mutant phenotype is associated with an increase in length of a poly(A) X poly(T) tract 222 base pairs (bp) upstream of the gene.
酿酒酵母有三个遗传位点编码不同的乙醇脱氢酶（ADH）同工酶：ADC1，编码经典的发酵同工酶ADHI；ADR2，编码受葡萄糖抑制的同工酶ADHII；以及ADM，编码一种与线粒体相关的ADH同工酶。当酵母在葡萄糖上生长时，ADC1基因表达，而ADR2基因被抑制。相反，在乙醇或甘油等非发酵碳源上生长会导致ADR2去抑制，而ADC1被抑制。ADC1和ADR2基因已被克隆和测序，并且鉴定出一些顺式作用突变，这些突变导致ADR2组成型表达，并且似乎分为两类。最常见的一类由不能完全去抑制且在可检测水平上不回复到野生型的突变体组成：这些是由一个转座元件插入到该基因的5'侧翼区域引起的。第二类突变体确实以可检测的频率回复到葡萄糖抑制的表型，并且当在非发酵碳源上生长时，将ADR2去抑制到高达野生型细胞中发现水平五倍的水平。我们在此报告两个这样的启动子上调、组成型ADR2突变体的5'侧翼区域的测序结果，在这两个突变体中，突变表型都与该基因上游222个碱基对（bp）处的一个聚（A）×聚（T）序列长度增加有关。
