Hashimoto H, Kikuchi Y, Nogi Y, Fukasawa T
Mol Gen Genet. 1983;191(1):31-8. doi: 10.1007/BF00330886.
The GAL4 gene positively regulating the expression of the gene cluster GAL7-GAL10-GAL1 in the yeast Saccharomyces cerevisiae was isolated for its ability to suppress a recessive mutation in that gene. When the isolated gene was incorporated into a multi-copy plasmid, the GAL cluster genes in the host chromosome partially escaped the normal control; a yeast that harbors the plasmid bearing the GAL4 gene synthesized the galactose-metabolizing enzymes encoded by the GAL cluster genes at a low but significant level in the absence of galactose. If the GAL7 gene was amplified along with GAL4 on the multi-copy plasmid, the constitutive synthesis of Gal-1-P uridylyl transferase encoded by GAL7 was further pronounced and the enzyme activity reached the level of the fully induced wild-type yeast. Such an escape synthesis of the GAL enzymes was not detected if GAL4 or both GAL4 and GAL7 were carried by a single-copy plasmid. The results suggest that the escape synthesis of GAL enzymes observed in the GAL4-amplified yeast was a consequence of overproduction of the GAL4 protein. The GAL80 gene negatively regulating the GAL cluster genes was also isolated, and when amplified together with GAL4, no escape synthesis of the GAL enzymes was observed, suggesting that the balanced synthesis of two regulatory proteins was essential to maintain the repressed state of the GAL cluster genes.
在酿酒酵母中，因能抑制该基因的隐性突变，分离出了正向调控基因簇GAL7 - GAL10 - GAL1表达的GAL4基因。当将分离出的该基因整合到多拷贝质粒中时，宿主染色体中的GAL基因簇部分逃脱了正常调控；携带含有GAL4基因质粒的酵母在无半乳糖的情况下，以低但显著的水平合成由GAL基因簇编码的半乳糖代谢酶。如果GAL7基因与GAL4一起在多拷贝质粒上扩增，由GAL7编码的Gal - 1 - P尿苷酰转移酶的组成型合成会进一步显著，且酶活性达到完全诱导的野生型酵母的水平。如果GAL4或GAL4和GAL7都由单拷贝质粒携带，则未检测到这种GAL酶的逃脱合成。结果表明，在GAL4扩增的酵母中观察到的GAL酶的逃脱合成是GAL4蛋白过量产生的结果。还分离出了负向调控GAL基因簇的GAL80基因，当它与GAL4一起扩增时，未观察到GAL酶的逃脱合成，这表明两种调控蛋白的平衡合成对于维持GAL基因簇的抑制状态至关重要。
