Figure 1
From: Distribution of fitness effects of mutations obtained from a simple genetic regulatory network model
Schematic of lac operon regulation. In E. coli, the repressor protein LacI (red) negatively regulates transcription of the lac operon by binding to its operator site in absence of lactose. However, due to imperfect binding (leaky expression) small amounts of LacY protein (yellow) is produced, which imports lactose molecules (blue) into the cell, when present in the environment. LacI then preferably binds the lactose molecule and forms the LacI-lactose complex, which can no longer bind the operator site of the lac operon. This results in the transcription of the lac genes which produce the lac proteins LacZ and LacY (green and yellow, respectively). The latter further increases the import of lactose molecules, which is metabolized by LacZ (green) into glucose (orange), and galactose molecules (brown).
