Transcriptional activation by artificial recruitment in mammalian cells

We show that the typical “nonclassical” activator, which comprises a fusion protein bearing a component of the transcriptional machinery fused to a DNA-binding domain, activates transcription in mammalian cells only weakly when tested with an array of promoters. However, as found in analogous “artificial recruitment” experiments performed in yeast, these activators work synergistically with “classical” activators. The effect of the classical activator in such experiments requires that it be tethered to DNA, a requirement that cannot be overcome by expression of that classical activator at high levels. The effect of the one nonclassical activator that does elicit significant levels of transcription when working alone (i.e., that bearing TATA box-binding protein) is strongly influenced by promoter architecture. The results, consistent with those of analogous experiments in yeast [see the accompanying paper: Gaudreau, L., Keaveney, M., Nevado, J., Zaman, Z., Bryant, G. O., Struhl, K. & Ptashne, M. (1999) Proc. Natl. Acad. Sci. USA 96, 2668–2673], suggest that classical activators, presumably by virtue of their abilities to interact with multiple targets, have a functional flexibility that nonclassical activators lack.

我们的研究表明，典型的“非经典”激活因子——即携带转录机器组分并与DNA结合结构域（DNA-binding domain）融合的融合蛋白——在以一系列启动子进行功能测试时，仅能微弱激活哺乳动物细胞中的转录过程。然而，正如酵母中开展的类似“人工招募”实验所得出的结论，这类非经典激活因子可与“经典”激活因子协同发挥转录激活作用。此类实验中，经典激活因子发挥效应的必要条件是其必须锚定至DNA分子上，即便通过高量表达该经典激活因子也无法规避这一要求。另有一类非经典激活因子在单独作用时可诱导显著水平的转录，即携带TATA盒结合蛋白（TATA box-binding protein）的激活因子，其转录激活效应受启动子结构的显著调控。本研究结果与酵母中同类实验的结论高度一致[详见同期论文：Gaudreau, L.、Keaveney, M.、Nevado, J.、Zaman, Z.、Bryant, G. O.、Struhl, K. & Ptashne, M. (1999) 美国国家科学院院刊(Proc. Natl. Acad. Sci. USA) 96, 2668–2673]，由此提示：经典激活因子大概率凭借其与多个靶标相互作用的能力，具备非经典激活因子所缺乏的功能灵活性。