Finley R L, West R W
Department of Biochemistry and Molecular Biology, SUNY Health Science Center, Syracuse 13210.
Mol Cell Biol. 1989 Oct;9(10):4282-90. doi: 10.1128/mcb.9.10.4282-4290.1989.
The upstream activating sequence of the adjacent and divergently transcribed GAL1 and GAL10 genes of Saccharomyces cerevisiae (UASG) contains at least three distinct classes of overlapping transcriptional control sites. The transcription activator GAL4 binds to four related sites in UASG and induces expression of GAL1 and GAL10 when galactose is available. We showed that UASG contains two additional positive control sites, designated GAL4/galactose-independent activating elements (GAEs), which reside at positions adjacent to or overlapping the GAL4-binding sites. When separated from neighboring sequences in UASG, the GAEs activate transcription independently of GAL4 with no requirement for galactose. In the intact GAL1-GAL10 divergent promoter region, their activity is ordinarily repressed by multiple negative control elements, the GAL operators. When galactose is available, GAL4 overcomes the activity of the GAL operators, while the putative GAE-binding proteins stay repressed. Combined, these results imply that distinct activators (GAL4 and GAE proteins) bound at adjacent or overlapping sites in UASG are differentially regulated by putative repressor proteins simultaneously bound at adjacent GAL operators. We surmise that GAE1 and GAE2 may have a physiological function other than regulation of galactose catabolism per se and discuss three hypotheses to account for their presence in UASG.
酿酒酵母相邻且转录方向相反的GAL1和GAL10基因的上游激活序列（UASG）包含至少三类不同的重叠转录控制位点。转录激活因子GAL4与UASG中的四个相关位点结合，并在有半乳糖时诱导GAL1和GAL10的表达。我们发现UASG包含另外两个正调控位点，称为GAL4/半乳糖非依赖性激活元件（GAEs），它们位于与GAL4结合位点相邻或重叠的位置。当从UASG中的相邻序列分离时，GAEs可独立于GAL4激活转录，且不需要半乳糖。在完整的GAL1 - GAL10双向启动子区域，它们的活性通常被多个负调控元件（GAL操纵子）抑制。当有半乳糖时，GAL4克服GAL操纵子的活性，而假定的GAE结合蛋白则保持被抑制状态。综合这些结果表明，结合在UASG中相邻或重叠位点的不同激活因子（GAL4和GAE蛋白）受到同时结合在相邻GAL操纵子上的假定阻遏蛋白的差异调节。我们推测GAE1和GAE2可能具有除调节半乳糖分解代谢本身之外的生理功能，并讨论了三种假说来解释它们在UASG中的存在。
