E. coli is "wise" enough to take suitable responding time, and suitable responding behaviors, when facing different kinds and intensities of stimulations. According to the time cost of a respond to a signal, we divide the intracellular processes into 2 levels: central dogma level and post translation level. The central dogma level includes the whole process of a gene transcribed to an mRNA then translated to a protein. The post translation level includes other intracellular process of non direct relation with genetic DNA or mRNA, for example protein-protein interaction, protein-metabolite interaction, protein localization, protein motion, etc. The time consuming for an action in the central dogma level is longer than that in the post translation level. In this study, firstly, we constructed a systematical network of glucose, PTS, glycogen and chemotaxis system, which was mediated by EI, HPr and ATP. This network plays a function as a switch, which controls E. coli's motion within the first few seconds. By using this switch, we unveiled a fact that the shorter time stimuli result in the post translation level reactions for quicker response. But further longer time stimuli will activate more time consuming the central dogma level reactions, that is this type of signals will be handled in the process of transcription or translation. Secondly, different intensities of signals result in different kinds of actions, was illustrated by ppGpp example. A low concentration ppGpp will cause RNAP express rRNA & table genes only; meanwhile, a high concentration ppGpp will cause RNAP express mRNA genes only. When E. coli is not in stringent occasion, without the binding of ppGpp, RNAP will express mRNA and other rRNA & stable genes in a proportion of 2:8. In all, a bacterium, like an E. coli, not only can identify different kinds of signals; but also can distinguish a signal's time-length and intensity, and then adopt different respond actions.
