Gene regulation by control of transcription has been analysed in great detail both in prokaryotes and in eukaryotes. The frequency of transcription may be decreased by repressors or increased by activators. A repressor may work by decreasing the concentration of RNA polymerase at a promoter capable of forming an open complex. An activator may work by increasing the concentration of RNA polymerase at a promoter capable of forming an open complex. For this purpose, a strategy is used over and over again. It is called increase in local concentration. How Escherichia coli uses this strategy efficiently is discussed.