Small S, Arnosti D N, Levine M
Department of Biology, UCSD, La Jolla 92093-0322.
Development. 1993 Nov;119(3):762-72.
The even-skipped (eve) promoter contains a series of enhancers that control the expression of different segmentation stripes in the Drosophila embryo. The stripe 3 enhancer is located 1.7 kb upstream of the stripe 2 enhancer. Here we demonstrate that these enhancers must be physically separated by a minimum distance for proper stripe expression. When they are directly coupled in either orientation, the enhancers generate abnormal patterns of expression in the early embryo. For example, the levels of stripe 2 expression are augmented and there is a posterior expansion of the pattern when the stripe 3 enhancer is positioned immediately upstream of the stripe 2 enhancer. Despite this spacing requirement, the order of the enhancers within the eve promoter can be reversed without affecting the normal expression pattern. These results suggest that spacing maintains the autonomous activities of the stripe enhancers and that interactions between enhancers can generate novel patterns of gene expression.
偶数缺口基因（eve）启动子包含一系列增强子，这些增强子控制果蝇胚胎中不同体节条纹的表达。条纹3增强子位于条纹2增强子上游1.7 kb处。我们在此证明，这些增强子必须在物理上相隔最小距离才能实现条纹的正常表达。当它们以任何一种方向直接连接时，增强子会在早期胚胎中产生异常的表达模式。例如，当条纹3增强子位于条纹2增强子的紧上游时，条纹2的表达水平会增加，并且模式会向后扩展。尽管有这种间隔要求，但eve启动子内增强子的顺序可以颠倒而不影响正常表达模式。这些结果表明，间隔维持了条纹增强子的自主活性，并且增强子之间的相互作用可以产生新的基因表达模式。
