Gray S, Cai H, Barolo S, Levine M
Department of Biology, University of California San Diego, La Jolla 92093, USA.
Philos Trans R Soc Lond B Biol Sci. 1995 Sep 29;349(1329):257-62. doi: 10.1098/rstb.1995.0111.
Transcriptional repression is essential for the conversion of crude maternal gradients into sharp territories of tissue differentiation in the Drosophila embryo. Evidence will be presented suggesting that some of the embryonic repressors function through a short-range 'quenching' mechanism, whereby a repressor works over short distances (ca. 50 b.p.) to block neighbouring activators within a target enhancer. This type of repression can explain how different enhancers work autonomously within complex modular promoters. However, at least one of the repressors operating in the early embryo works through a long-range, or silencing, mechanism. The binding of a silencer to a given enhancer leads to the inactivation of all enhancers within a complex promoter. The analysis of chromatin boundary elements suggest that silencers and enhancers might work through distinct mechanisms. We speculate that silencers constrain the evolution of complex promoters.
转录抑制对于果蝇胚胎中原始母体梯度转化为组织分化的清晰区域至关重要。将提供证据表明，一些胚胎抑制因子通过短程“淬灭”机制发挥作用，即抑制因子在短距离（约50个碱基对）内起作用，以阻断靶增强子内相邻的激活因子。这种类型的抑制可以解释不同的增强子如何在复杂的模块化启动子内自主发挥作用。然而，至少有一种在早期胚胎中起作用的抑制因子是通过长程或沉默机制发挥作用的。沉默子与特定增强子的结合会导致复杂启动子内所有增强子失活。对染色质边界元件的分析表明，沉默子和增强子可能通过不同的机制发挥作用。我们推测沉默子限制了复杂启动子的进化。
