Lightfoot K, Maltby L, Duarte R, Veale R, Segev O
Department of Zoology, University of the Witwatersrand, South Africa.
Br J Cancer. 1994 Feb;69(2):264-73. doi: 10.1038/bjc.1994.50.
The Drosophila ras2 promoter region exhibits bidirectional activity, as has been demonstrated for the human c-Ha-ras1 and the mouse c-Ki-ras. Here we address a unique case of ras regulation, as Drosophila ras2 provides the only example to date in which the flanking gene (rop) and its product have been isolated. A linking mechanism of control suggests a mutual interaction between the two gene products. Our studies indicate that the Drosophila ras2 promoter region shares with the human c-Ha-ras1 promoter a CACCC box and an AP-1-like sequence. A 14 bp promoter fragment which holds a CACCC element is demonstrated to interact with a specific transcription factor (factor B). This CACCC promoter element represents a stretch of imperfect palindrome. We present evidence that this factor can form a complex with another specific DNA-binding protein (factor A). The binding sites (A + B) for these protein factors are essential for 95% expression of both genes flanking the promoter (ras2 and rop). Region A consists of four overlapping consensus sequences: a TATA-like element, a DSE-like motif (the core sequence of the serum response element), a DRE octamer, which has been shown to play a role in cell proliferation, and a 5 bp direct repeat representing the GATA consensus sequence. Factor A has a very weak affinity to the full promoter region, but when complexed with factor B binding efficiency is enhanced. We also show that alterations of DNA-protein binding specificities can be achieved by supplementing the growth media with different sera.
果蝇ras2启动子区域表现出双向活性，这已在人类c-Ha-ras1和小鼠c-Ki-ras中得到证实。在此，我们探讨ras调控的一个独特案例，因为果蝇ras2是迄今为止唯一的一个侧翼基因（rop）及其产物已被分离的例子。一种控制的连接机制表明这两种基因产物之间存在相互作用。我们的研究表明，果蝇ras2启动子区域与人类c-Ha-ras1启动子共有一个CACCC框和一个AP-1样序列。一个包含CACCC元件的14bp启动子片段被证明可与一种特定转录因子（因子B）相互作用。这个CACCC启动子元件代表一段不完全回文序列。我们提供的证据表明，该因子可与另一种特定的DNA结合蛋白（因子A）形成复合物。这些蛋白质因子的结合位点（A + B）对于启动子两侧的两个基因（ras2和rop）95%的表达至关重要。区域A由四个重叠的共有序列组成：一个类似TATA的元件、一个类似DSE的基序（血清反应元件的核心序列）、一个DRE八聚体（已证明其在细胞增殖中起作用）以及一个代表GATA共有序列的5bp直接重复序列。因子A对整个启动子区域的亲和力非常弱，但与因子B形成复合物时结合效率会提高。我们还表明，通过在生长培养基中添加不同血清可以实现DNA-蛋白质结合特异性的改变。
