Winston M K, Bhattacharjee J K
Department of Microbiology, Miami University, Oxford, OH 45056.
Curr Genet. 1987;11(5):393-8. doi: 10.1007/BF00378182.
Derepression of lysine biosynthetic enzymes of Saccharomyces cerevisiae was investigated in lys9 auxotrophs which lack saccharopine reductase activity. Five enzymes (homocitrate synthase, homoisocitrate dehydrogenase, alpha-aminoadipate aminotransferase, alpha-aminoadipate reductase and saccharopine dehydrogenase) were constitutively derepressed in all lys9 mutants with up to eight-fold higher enzyme levels than in isogenic wild-type cells. Levels of these enzymes in lys2, lys14, and lys15 mutants were the same or lower than those in wild-type cells. The regulatory property of lys9 mutants exhibited recessiveness to the wild-type gene in heterozygous diploids. Unlike the mating type effect, homozygous diploids resulting from crosses between lys9 auxotrophs exhibited even higher levels of derepressed enzymes than the haploid mutants. Addition of a higher concentration of lysine to the growth medium resulted in reduction of enzyme levels although they were still derepressed. These results suggest that lys9 mutants represent a lesion for the saccharopine reductase and may represent a repressor mutation which in the wild-type cells simultaneously represses unlinked structural genes that encode for five of the lysine biosynthetic enzymes.
在缺乏酵母氨酸还原酶活性的lys9营养缺陷型中，对酿酒酵母赖氨酸生物合成酶的去阻遏作用进行了研究。在所有lys9突变体中，五种酶（高柠檬酸合酶、高异柠檬酸脱氢酶、α-氨基己二酸转氨酶、α-氨基己二酸还原酶和酵母氨酸脱氢酶）组成型去阻遏，其酶水平比同基因野生型细胞高八倍。lys2、lys14和lys15突变体中这些酶的水平与野生型细胞中的相同或更低。lys9突变体的调控特性在杂合二倍体中对野生型基因表现出隐性。与交配型效应不同，lys9营养缺陷型之间杂交产生的纯合二倍体表现出比单倍体突变体更高水平的去阻遏酶。向生长培养基中添加更高浓度的赖氨酸会导致酶水平降低，尽管它们仍然处于去阻遏状态。这些结果表明，lys9突变体代表了酵母氨酸还原酶的一个损伤，可能代表一种阻遏突变，在野生型细胞中，该突变同时阻遏编码五种赖氨酸生物合成酶的不连锁结构基因。
