Boulden A, Sealy L
Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, Tennessee 37232.
Virology. 1990 Jan;174(1):204-16. doi: 10.1016/0042-6822(90)90069-4.
We have identified a new protein factor (EFIII) in nuclear extracts of quail fibroblasts and chick embryos which binds specifically in vitro to a 26-bp region of the Rous sarcoma virus (RSV) long terminal repeat (LTR) enhancer. The EFIII binding site in the RSV LTR exhibits a strong sequence homology to the serum response element (SRE). The SRE is a 22-bp cis-acting DNA sequence element, first identified upstream of the human c-fos gene, which can confer serum inducibility to heterologous promotors. The binding site for EFIII in the RSV LTR enhancer is also of interest because this region has been implicated in mediating trans-activation of the RSV LTR enhancer by the protein product of the v-fos gene. We show that avian EFIII binds with equal efficiency to both its binding sites in the RSV LTR and the human c-fos SRE. A dyad symmetry element in the c-fos SRE, previously shown to be critical for binding of the cognate human serum response factor (SRF), is also critical for EFIII binding to the LTR SRE-homologous sequences; similarly, EFIII and the human SRF exhibit identical protein-DNA contacts with their corresponding recognition sequences. We suggest that EFIII may be the avian homolog of the mammalian SRF and, in fact, have evidence to indicate that the RSV LTR is serum responsive.
我们在鹌鹑成纤维细胞和鸡胚的核提取物中鉴定出一种新的蛋白质因子（EFIII），它在体外能特异性结合劳氏肉瘤病毒（RSV）长末端重复序列（LTR）增强子的一个26bp区域。RSV LTR中的EFIII结合位点与血清反应元件（SRE）具有很强的序列同源性。SRE是一个22bp的顺式作用DNA序列元件，最初在人c-fos基因上游被鉴定出来，它能赋予异源启动子血清诱导性。RSV LTR增强子中EFIII的结合位点也很有趣，因为该区域与v-fos基因的蛋白质产物介导RSV LTR增强子的反式激活有关。我们发现禽类EFIII能以相同效率结合RSV LTR及其人c-fos SRE中的两个结合位点。c-fos SRE中的一个二元对称元件，先前已证明对同源人血清反应因子（SRF）的结合至关重要，对EFIII结合LTR SRE同源序列也至关重要；同样，EFIII和人SRF与它们相应的识别序列表现出相同的蛋白质-DNA相互作用。我们认为EFIII可能是哺乳动物SRF的禽类同源物，事实上，我们有证据表明RSV LTR对血清有反应。
