Stone G, Sadowski I
Department of Biochemistry, University of British Columbia, Vancouver, Canada.
EMBO J. 1993 Apr;12(4):1375-85. doi: 10.1002/j.1460-2075.1993.tb05782.x.
The Saccharomyces cerevisiae transcriptional activator GAL4 is regulated by the presence of available carbon sources. Galactose induces activity by inhibiting the negative regulator GAL80, while glucose, the preferred carbon source, antagonizes GAL4 function by several mechanisms. In the present study we present evidence that one mechanisms for inhibition of GAL transcription by glucose involves direct inhibition of the GAL4 protein. We demonstrate that a large, previously uncharacterized, central region of GAL4 contains at least three 'inhibitory domains' and a 'glucose response domain' (GRD). Deletion of the entire central region eliminates direct inhibition of GAL4 by glucose, and furthermore, fusion of the central region to a heterologous transcriptional activator confers inhibition by glucose. The central region inhibitory domains constitutively inhibit transcriptional activation when the GRD is absent. Direct inhibition of GAL4 activity can be detected within 30 min following glucose addition and may represent an early mechanism promoting a switch from galactose to glucose utilization. A model for the regulatory role of the central region is presented, involving interaction with an additional protein that inhibits GAL4 activity when glucose is present.
酿酒酵母转录激活因子GAL4受可用碳源的调控。半乳糖通过抑制负调控因子GAL80来诱导活性，而葡萄糖作为首选碳源，则通过多种机制拮抗GAL4的功能。在本研究中，我们提供证据表明，葡萄糖抑制GAL转录的一种机制涉及对GAL4蛋白的直接抑制。我们证明，GAL4一个大的、以前未被表征的中央区域至少包含三个“抑制结构域”和一个“葡萄糖反应结构域”（GRD）。删除整个中央区域可消除葡萄糖对GAL4的直接抑制，此外，将中央区域与异源转录激活因子融合会赋予葡萄糖抑制作用。当不存在GRD时，中央区域抑制结构域会组成性地抑制转录激活。在添加葡萄糖后30分钟内即可检测到对GAL4活性的直接抑制，这可能代表了促进从半乳糖利用向葡萄糖利用转变的早期机制。本文提出了一个关于中央区域调控作用的模型，该模型涉及与另一种蛋白质的相互作用，这种蛋白质在有葡萄糖存在时会抑制GAL4的活性。
