Figure 1
From: A framework and model system to investigate linear system behavior in Escherichia coli

Black box representation of the E. coli transcriptional system. A. Genetic devices (synthetic and native) in the form of DNA act as inputs to the system, with the resultant RNA produced the output. B. Pictorial depiction of the superposition principle in effect in linear systems. Superposition states that the output from a set of inputs represents the linear sum of the outputs from each individual input.