Enhancer(激活元件): a given site binds regulator responsible for activating the gene. Alternative enhancer binds different groups of regulators and control expression of the same gene at different times and places in responsible to different signals Activation at a distance is much more common in eukaryotes. Insulators(绝缘子) or boundary elements(临界元 f)are regulatory sequences between enhancers and promoters. They block activation of a linked promoter by activator bound at the enhancer and therefore ensure activators work discriminately11 Enhancer (激活元件) : a given site binds regulator responsible for activating the gene. Alternative enhancer binds different groups of regulators and control expression of the same gene at different times and places in responsible to different signals. Activation at a distance is much more common in eukaryotes. Insulators (绝缘子) or boundary elements (临界元 件) are regulatory sequences between enhancers and promoters. They block activation of a linked promoter by activator bound at the enhancer, and therefore ensure activators work discriminately