Baker S M, Johnston S A, Hopper J E, Jaehning J A
Mol Gen Genet. 1987 Jun;208(1-2):127-34. doi: 10.1007/BF00330433.
High levels of the GAL7 gene in the yeast cell appear to titrate regulatory factors and to impair transcription of related sequences. To investigate the role that the GAL regulatory factors GAL4 and GAL80 have in this process we have compared the accumulation of mRNA transcribed from single-copy (plasmid-borne GAL7 and chromosomal GAL10) and high-copy (plasmid-borne GAL7) genes in several GAL regulatory mutants. Our results show that functional GAL4 gene product is required for induction of transcription from the single- and high-copy genes. In a strain containing the GAL4 gene fused to the high expression ADH1 promoter, glucose can replace galactose to induce high levels of transcription of GAL7 and GAL10 genes, although the kinetics of accumulation induced by the two sugars are distinctly different. In the presence of high levels of GAL4, maximum accumulation of mRNA from single and high copy genes is elevated two-fold; disruption of the gal80 gene in combination with high levels of GAL4 results in a further two-fold increase in transcription. In this genetic background, galactose-induced transcription of the high copy GAL7 gene results in a greater than 50-fold increase in the levels of GAL7 mRNA, representing 30%-50% of the total cellular mRNA. Our results are consistent with a cooperative effect of saturation of multiple GAL4 DNA binding sites and with a limiting factor, in addition to GAL4, that is required for transcription of the GAL genes.
酵母细胞中高水平的GAL7基因似乎会消耗调控因子并损害相关序列的转录。为了研究GAL调控因子GAL4和GAL80在此过程中的作用，我们比较了几种GAL调控突变体中从单拷贝（质粒携带的GAL7和染色体上的GAL10）和高拷贝（质粒携带的GAL7）基因转录的mRNA的积累情况。我们的结果表明，功能性GAL4基因产物是诱导单拷贝和高拷贝基因转录所必需的。在一个含有与高表达ADH1启动子融合的GAL4基因的菌株中，葡萄糖可以替代半乳糖来诱导GAL7和GAL10基因的高水平转录，尽管两种糖诱导积累的动力学明显不同。在高水平GAL4存在的情况下，单拷贝和高拷贝基因的mRNA最大积累量提高了两倍；在高水平GAL4的情况下破坏gal80基因会导致转录进一步增加两倍。在这种遗传背景下，半乳糖诱导的高拷贝GAL7基因转录导致GAL7 mRNA水平增加超过50倍，占细胞总mRNA的30%-50%。我们的结果与多个GAL4 DNA结合位点饱和的协同效应以及除GAL4之外GAL基因转录所需的限制因子一致。
