Qian S, Varjavand B, Pirrotta V
Department of Cell Biology, Baylor College of Medicine, Houston, Texas 77030.
Genetics. 1992 May;131(1):79-90. doi: 10.1093/genetics/131.1.79.
We have analyzed the eye and testis enhancers located 1 kb upstream of the transcription start site of the white gene. Both enhancers confer the corresponding tissue-specific expression on a heterologous promoter as well as on the white promoter. The eye determinant consists of multiple elements, each able to stimulate eye-specific expression. It also contains five binding sites for the zeste protein while the immediately adjacent testis element contains none. Site-directed mutation of these zeste binding sites abolishes the zeste-white interaction but does not significantly affect the eye enhancer activity, indicating that they are not important for the eye enhancer activity per se. Other zeste binding sites just upstream of the promoter are not necessary for the zeste-white interaction. We conclude that the overlap of the eye enhancer with the zeste binding sites is responsible for the zeste-white interaction and explains why this interaction affects eye but not testis expression. Sequence deletion or substitution experiments suggested that the white promoter is internal to the transcription start site; the zeste protein is not required for distant enhancer action but a 95-bp promoter-proximal sequence is essential for distant enhancer-promoter interaction. This element may serve as an anchor to stabilize formation of a loop that brings the enhancer to the vicinity of the promoter.
我们分析了位于白色基因转录起始位点上游1 kb处的眼睛和睾丸增强子。这两种增强子均能赋予异源启动子以及白色基因启动子相应的组织特异性表达。眼睛决定因素由多个元件组成，每个元件都能刺激眼睛特异性表达。它还包含五个与zeste蛋白的结合位点，而紧邻的睾丸元件则不包含。这些zeste结合位点的定点突变消除了zeste与白色基因的相互作用，但并未显著影响眼睛增强子的活性，这表明它们本身对眼睛增强子活性并不重要。启动子上游的其他zeste结合位点对于zeste与白色基因的相互作用并非必需。我们得出结论，眼睛增强子与zeste结合位点的重叠是zeste与白色基因相互作用的原因，并解释了为什么这种相互作用影响眼睛而非睾丸的表达。序列缺失或替换实验表明，白色基因启动子位于转录起始位点内部；zeste蛋白对于远距离增强子作用并非必需，但一个95 bp的启动子近端序列对于远距离增强子与启动子的相互作用至关重要。该元件可能作为一个锚点，稳定将增强子带到启动子附近的环的形成。
