Florence B, Guichet A, Ephrussi A, Laughon A
Department of Genetics, University of Wisconsin, Madison 53706, USA.
Development. 1997 Feb;124(4):839-47. doi: 10.1242/dev.124.4.839.
The fushi tarazu pair-rule gene is required for the formation of alternating parasegmental boundaries in the Drosophila embryo. fushi tarazu encodes a homeodomain protein necessary for transcription of the engrailed gene in even-numbered parasegments. Here we report that, within an engrailed enhancer, adjacent and conserved binding sites for the Fushi tarazu protein and a cofactor are each necessary, and together sufficient, for transcriptional activation. Footprinting shows that the cofactor site can be bound specifically by Ftz-F1, a member of the nuclear receptor superfamily. Ftz-F1 and the Fushi tarazu homeodomain bind the sites with 4- to 8-fold cooperativity, suggesting that direct contact between the two proteins may contribute to target recognition. Even parasegmental reporter expression is dependent on Fushi tarazu and maternal Ftz-F1, suggesting that these two proteins are indeed the factors that act upon the two sites in embryos. The two adjacent binding sites are also required for continued activity of the engrailed enhancer after Fushi tarazu protein is no longer detectable, including the period when engrailed, and the enhancer, become dependent upon wingless. We also report the existence of a separate negative regulatory element that apparently responds to odd-skipped.
腹节基因缺失配对规则基因对于果蝇胚胎中交替副节边界的形成是必需的。腹节基因缺失编码一种同源异型结构域蛋白，该蛋白对于偶数副节中 engrailed 基因的转录是必需的。在此我们报道，在 engrailed 增强子内，腹节基因缺失蛋白和一个辅助因子的相邻且保守的结合位点对于转录激活而言各自都是必需的，且二者共同作用时是充分的。足迹法表明辅助因子位点可被核受体超家族成员 Ftz-F1 特异性结合。Ftz-F1 和腹节基因缺失同源异型结构域以 4 至 8 倍的协同性结合这些位点，这表明这两种蛋白之间的直接接触可能有助于靶标识别。偶数副节报告基因的表达依赖于腹节基因缺失和母体 Ftz-F1，这表明这两种蛋白确实是在胚胎中作用于这两个位点的因子。在腹节基因缺失蛋白不再可检测到之后，包括 engrailed 和增强子变得依赖于无翅基因的时期，这两个相邻的结合位点对于 engrailed 增强子的持续活性也是必需的。我们还报道了一个单独的负调控元件的存在，该元件显然对奇数缺失基因有反应。
