Function of positive regulatory gene gal4 in the synthesis of galactose pathway enzymes in Saccharomyces cerevisiae: evidence that the GAL81 region codes for part of the gal4 protein
Function of positive regulatory gene gal4 in the synthesis of galactose pathway enzymes in Saccharomyces cerevisiae: evidence that the GAL81 region codes for part of the gal4 protein
复制标题
正调控基因 gal4 在酿酒酵母半乳糖途径酶合成中的功能：GAL81 区域编码部分 gal4 蛋白的证据
作者：
K. Matsumoto;Y. Adachi;A. Toh;Y. Oshima
构建了 gal4 基因座的减数分裂精细结构图，该图在染色体上延伸超过 0.44 个单位（单位以假定重组的百分比频率表示）。几个无义 gal4 突变（四个 UAA 和两个假定的 UGA [gal4-62 和 gal4-69]）被放置在图谱上的不同位点。在20个独立分离的gal4突变体的回复实验中，只有位于图谱上同一位点的gal4-62和gal4-69等位基因可以自发回复以克服gal80s-1的超抑制，频率约为4 x 10(-7)。回复体的二次突变发生在 gal4-62 区域，或者是由不相关的抑制子引起的。借助gal4突变体的三点杂交，发现19个分离株中共有15个GAL81突变与gal4-62位于同一区域；其他四个无法分析。恢复的 gal4 基因和 GAL81 突变对野生型 GAL4+ 等位基因具有半显性，并且对无义 gal4 突变具有完全显性。分离出四个对 gal4-62 和 gal4-69 有效的抑制因子（一个显性的和三个隐性的）。显性抑制子还对三个独立的、真正的营养缺陷型UGA无义突变有效，并且三个隐性抑制子之一对真正的营养缺陷型UAA和UAG突变有效。这些结果有力地支持了以下观点：gal4 基因座是组成型表达并编码调节蛋白。 GAL81 位点映射在 gal4 蛋白一部分的基因座编码内，但不能作为操纵子发挥作用。
A meiotic fine structure map of the gal4 locus was constructed, which extended over 0.44 units on the chromosome (units in percent frequency of supposed recombination). Several nonsense gal4 mutations (four UAA and two supposed UGA [gal4-62 and gal4-69]) were placed at various sites on the map. In reversion experiments with 20 independently isolated gal4 mutants, only the gal4-62 and gal4-69 alleles, which are located at the same site on the map, could revert to overcome the superrepression of gal80s-1 spontaneously with a frequency of approximately 4 x 10(-7). Secondary mutations in the revertants occurred in the region of gal4-62 or were due to unlinked suppressors. A total of 15 GAL81 mutations in 19 isolates were found to be located in the same region as gal4-62 by three-point crosses with the aid of gal4 mutants; the other four could not be analyzed. The reverted gal4 gene and GAL81 mutations were semidominant over the wild-type GAL4+ allele and fully dominant over a nonsense gal4 mutation. Four suppressors (one dominant and three recessive) effective against gal4-62 and gal4-69 were isolated. The dominant suppressor was also effective against three independent, authentic auxotrophic UGA nonsense mutations, and one of the three recessive suppressors were effective against the authentic auxotrophic UAA and UAG mutations. These results strongly support the idea that the gal4 locus is expressed constitutively and codes for a regulatory protein. The GAL81 site mapped inside the locus codes for a part of the gal4 protein but does not work as an operator.