Department of Molecular Cell Biology, Weizmann Institute of Science, Rehovot 76100, Israel.
Mol Cell. 2012 May 25;46(4):399-407. doi: 10.1016/j.molcel.2012.04.032.
A gene can be said to be insulated from environmental variations if its expression level depends only on its cognate inducers, and not on variations in conditions. We tested the insulation of the lac promoter of E. coli and of synthetic constructs in which the transcription factor CRP acts as either an activator or a repressor, by measuring their input function-their expression as a function of inducers-in different growth conditions. We find that the promoter activities show sizable variation across conditions of 10%-100% (SD/mean). When the promoter is bound to its cognate regulator(s), variation across conditions is smaller than when it is unbound. Thus, mode of regulation affects insulation: activators seem to show better insulation at high expression levels, and repressors at low expression levels. This may explain the Savageau demand rule, in which E. coli genes needed often in the natural environment tend to be regulated by activators, and rarely needed genes by repressors. The present approach can be used to study insulation in other genes and organisms.
如果一个基因的表达水平仅依赖于其同源诱导物，而不依赖于条件的变化，那么可以说该基因与环境变化隔离开来。我们通过测量它们的输入函数（作为诱导物函数的表达），即在不同生长条件下的表达，来测试大肠杆菌的 lac 启动子和作为激活剂或抑制剂的合成构建体的隔离性。我们发现启动子活性在 10％-100％（SD/均值）的条件下有很大的变化。当启动子与其同源调节剂结合时，条件之间的变化小于未结合时的变化。因此，调节方式会影响隔离性：在高表达水平下，激活剂似乎表现出更好的隔离性，而在低表达水平下，抑制剂则表现出更好的隔离性。这可能解释了 Savageau 需求规则，即在自然环境中经常需要的大肠杆菌基因往往由激活剂调节，而很少需要的基因则由抑制剂调节。本方法可用于研究其他基因和生物的隔离性。
