Wang J C, Van Dyke M W
Department of Tumor Biology, University of Texas M.D. Anderson Cancer Center, Houston 77030.
Biochim Biophys Acta. 1994 Aug 2;1218(3):308-14. doi: 10.1016/0167-4781(94)90182-1.
One way specific transcription factors are thought to activate transcription initiation is by facilitating interactions between the general transcription factor TFIID and DNA sequences downstream of the TATA element. Examples supporting this model include transcription activation from the core adenovirus E4 promoter by either the human gene-specific transcription factor ATF or the acidic-domain fusion protein GAL4-AH. In these cases, appearance of downstream promoter binding by TFIID correlated directly with transcription activation by these proteins. Previously we had shown that downstream promoter binding by TFIID involved recognition of the initiator DNA control element and that the extent of this binding correlated directly with initiator-dependent transcription activation in vitro. We now report our use of DNase I footprinting and in vitro transcription to investigate the effects of various stimulatory transcription factors on TFIID binding and transcription efficiency from different initiator-containing promoters. Transcription factors investigated included Sp1, USF, and several GAL4-acidic domain fusion proteins. We found that none of these transcription factors appreciably affected downstream promoter binding by TFIID, whether qualitatively or quantitatively. In fact, all of these transcription factors stimulated transcription in vitro regardless of the strength of the initiator element present. When both elements were present, transcription stimulation mediated by proximally bound transcription factors and by TFIID-initiator interaction seemed to be synergistic. Taken together, our data would suggest that transcription activation by these two means occurs through different steps within the transcriptional process.
一种认为特异性转录因子激活转录起始的方式是通过促进通用转录因子TFIID与TATA元件下游的DNA序列之间的相互作用。支持该模型的例子包括人基因特异性转录因子ATF或酸性结构域融合蛋白GAL4-AH从核心腺病毒E4启动子激活转录。在这些情况下，TFIID对下游启动子的结合出现与这些蛋白的转录激活直接相关。此前我们已经表明，TFIID对下游启动子的结合涉及对起始子DNA控制元件的识别，并且这种结合的程度与体外起始子依赖性转录激活直接相关。我们现在报告我们使用DNA酶I足迹法和体外转录来研究各种刺激性转录因子对来自不同含起始子启动子的TFIID结合和转录效率的影响。研究的转录因子包括Sp1、USF和几种GAL4-酸性结构域融合蛋白。我们发现，无论在定性还是定量方面，这些转录因子均未明显影响TFIID对下游启动子的结合。事实上，所有这些转录因子在体外均能刺激转录，而与存在的起始子元件的强度无关。当两种元件都存在时，近端结合的转录因子和TFIID-起始子相互作用介导的转录刺激似乎是协同的。综上所述，我们的数据表明这两种方式的转录激活是通过转录过程中的不同步骤发生的。
