West R W, Chen S M, Putz H, Butler G, Banerjee M
Department of Biochemistry and Molecular Biology, SUNY Health Science Center, Syracuse 13210.
Genes Dev. 1987 Dec;1(10):1118-31. doi: 10.1101/gad.1.10.1118.
The upstream activating sequence (UASG) of the adjacent and divergently transcribed GAL1 and GAL10 promoters of Saccharomyces cerevisiae regulates the induction of the corresponding genes in response to the presence of galactose. We constructed chimeric yeast promoters in which a different UAS, UASC from the iso-1-cytochrome c (CYC1) gene of S. cerevisiae, was fused at different locations upstream of GAL1 (UASC-GAL1 promoters) or GAL10 (UASC-GAL10 promoters) and used to monitor the activity of UASG in cells grown in the presence or absence of galactose. Though the CYC1 promoter is fully induced in yeast grown in glycerol medium, UASC-GAL chimeric promoters containing UASG were repressed as much as 400-fold (UASC-GAL1) or 1350-fold (UASC-GAL10) in this growth medium. Several distinct portions of the GAL1-GAL10 divergent promoter region blocked the UASC-induced expression of the GAL1 and GAL10 promoters, whereas others did not, suggesting that several distinct negative control elements are present that may repress transcription of GAL1 and GAL10 in the absence of galactose. The approximate locations of these negative control elements were delimited to sites adjacent to or possibly overlapping the sites at which the positive control protein GAL4 binds in UASG. Deletion derivatives of GAL4 that fail to induce transcription from the wild-type GAL promoters but retain the DNA binding domain significantly derepressed the expression of the UASC-GAL chimeric promoters. These results, combined with those of earlier studies, suggest the possibility that GAL4 normally induces transcription of GAL1 and GAL10 by blocking the activity of these negative control elements, in addition to stimulating transcription by a mechanism of positive control.
酿酒酵母相邻且转录方向相反的GAL1和GAL10启动子的上游激活序列（UASG）可调节相应基因在半乳糖存在时的诱导表达。我们构建了嵌合酵母启动子，其中来自酿酒酵母同工酶-1-细胞色素c（CYC1）基因的不同UAS（UASC）在GAL1（UASC-GAL1启动子）或GAL10（UASC-GAL10启动子）上游的不同位置融合，并用于监测UASG在有或无半乳糖情况下生长的细胞中的活性。尽管CYC1启动子在甘油培养基中生长的酵母中被完全诱导，但在这种生长培养基中，含有UASG的UASC-GAL嵌合启动子被抑制了多达400倍（UASC-GAL1）或1350倍（UASC-GAL10）。GAL1-GAL10反向启动子区域的几个不同部分阻断了UASC诱导的GAL1和GAL10启动子的表达，而其他部分则没有，这表明存在几个不同的负调控元件，它们可能在无半乳糖时抑制GAL1和GAL10的转录。这些负调控元件的大致位置被限定在与UASG中阳性对照蛋白GAL4结合位点相邻或可能重叠的位点。不能从野生型GAL启动子诱导转录但保留DNA结合结构域的GAL4缺失衍生物显著解除了UASC-GAL嵌合启动子的表达抑制。这些结果与早期研究结果相结合，表明除了通过正调控机制刺激转录外，GAL4通常还通过阻断这些负调控元件的活性来诱导GAL1和GAL10的转录。
