McStay B, Sullivan G J, Cairns C
Biomedical Research Centre, University of Dundee, UK.
EMBO J. 1997 Jan 15;16(2):396-405. doi: 10.1093/emboj/16.2.396.
Repeated sequence elements found upstream of the ribosomal gene promoter in Xenopus function as RNA polymerase I-specific transcriptional enhancers. Here we describe an in vitro system in which these enhancers function in many respects as in vivo. The principal requirement for enhancer function in vitro is the presence of a high concentration of upstream binding factor (UBF). This system is utilized to demonstrate that enhancers function by increasing the probability of a stable transcription complex forming on the adjacent promoter. Species differences in UBF are utilized to demonstrate that enhancers do not act by recruiting UBF to the promoter, rather UBF performs its own distinct role at the enhancers. UBF function in enhancement differs from that at the promoter, as it is flexible with respect to both the species of UBF and the enhancer element employed. Additionally, we identify a potential role for the mammalian UBF splice variant, UBF2, in enhancer function. We demonstrate that the TATA box binding protein (TBP)-containing component of Xenopus RNA polymerase I transcription, Rib1, can interact with an enhancer-UBF complex. This suggests a model in which enhancers act by recruiting Rib1 to the promoter.
在非洲爪蟾核糖体基因启动子上游发现的重复序列元件可作为RNA聚合酶I特异性转录增强子发挥作用。在此，我们描述了一种体外系统，在该系统中这些增强子在许多方面的功能与在体内时相同。体外增强子功能的主要要求是存在高浓度的上游结合因子（UBF）。利用该系统可证明增强子通过增加在相邻启动子上形成稳定转录复合物的概率来发挥作用。利用UBF中的物种差异可证明增强子并非通过将UBF招募至启动子来发挥作用，而是UBF在增强子处发挥其独特的作用。UBF在增强作用中的功能与在启动子处不同，因为它在所用的UBF物种和增强子元件方面都具有灵活性。此外，我们确定了哺乳动物UBF剪接变体UBF2在增强子功能中的潜在作用。我们证明，非洲爪蟾RNA聚合酶I转录中含TATA盒结合蛋白（TBP）的成分Rib1可与增强子-UBF复合物相互作用。这提示了一种模型，即增强子通过将Rib1招募至启动子来发挥作用。
