Xiao H, Jeang K T
Molecular Virology Section, Laboratory of Molecular Microbiology, NIAID, National Institutes of Health, Bethesda, Maryland 20892-0460, USA.
J Biol Chem. 1998 Sep 4;273(36):22873-6. doi: 10.1074/jbc.273.36.22873.
Activation domains of eukaryotic transcription factors can be classified into at least three distinct types based on their amino acid composition: acidic, proline-rich, and glutamine-rich. Acidic activators, such as yeast GAL4 and GCN4 and herpes simplex virus VP16, have been shown to stimulate transcription in various higher and lower eukaryotic cells. Similarly, proline-rich activators also function in both mammalian and yeast cells. These activators are regarded to possess "universal" activating potentials. By contrast, several studies have suggested that glutamine-rich activators such as human Sp1 are active in higher (mammalian) but not lower (yeast) eukaryotic cells. One interpretation is that lower eukaryotic cells lack a critical co-factor necessary for a glutamine-rich domain. This reasoning is counter-intuitive because many native yeast activator proteins contain glutamine-rich domains. Here, we have investigated the activity of a glutamine-rich GAL4-Sp1 domain A (Sp1A) hybrid protein in yeast Saccharomyces cerevisiae. We show that GAL4-Sp1A activated a GAL1-lacZ reporter by more than 200-fold over basal when the reporter was carried on a 2mu vector. The generality of the Sp1A results is supported by our finding that yeast glutamine-rich domains from HAP2 and MCM1 are also transcriptionally active in S. cerevisiae. Interestingly, we found that glutamine-rich domains are considerably less potent when responsive promoters (i.e. GAL1-lacZ) are integrated into yeast chromosome. Thus our results segregate the inherent transcriptional activity of a glutamine-rich domain in yeast S. cerevisiae from its apparent lack of activity when assayed on chromosomally embedded promoters.
基于氨基酸组成，真核转录因子的激活结构域可至少分为三种不同类型：酸性结构域、富含脯氨酸结构域和富含谷氨酰胺结构域。酸性激活因子，如酵母GAL4和GCN4以及单纯疱疹病毒VP16，已被证明能在各种高等和低等真核细胞中刺激转录。同样，富含脯氨酸的激活因子在哺乳动物细胞和酵母细胞中均有作用。这些激活因子被认为具有“通用”的激活潜力。相比之下，多项研究表明，富含谷氨酰胺的激活因子，如人类Sp1，在高等（哺乳动物）而非低等（酵母）真核细胞中具有活性。一种解释是，低等真核细胞缺乏富含谷氨酰胺结构域所需的关键辅助因子。这种推理有违直觉，因为许多天然酵母激活蛋白都含有富含谷氨酰胺的结构域。在此，我们研究了富含谷氨酰胺的GAL4-Sp1结构域A（Sp1A）杂交蛋白在酿酒酵母中的活性。我们发现，当报告基因载体为2μm质粒时，GAL4-Sp1A激活GAL1-lacZ报告基因的能力比基础水平高出200多倍。我们发现来自HAP2和MCM1的酵母富含谷氨酰胺结构域在酿酒酵母中也具有转录活性，这支持了Sp1A结果的普遍性。有趣的是，我们发现当反应性启动子（即GAL1-lacZ）整合到酵母染色体中时，富含谷氨酰胺的结构域的活性会显著降低。因此，我们的结果将酿酒酵母中富含谷氨酰胺结构域的固有转录活性与其在染色体嵌入启动子上检测时明显缺乏的活性区分开来。
