To obtain regulated promoters we synthesized four libraries of operator sequences, respectively for LacI, TetR, CI and LexA repressor proteins. In each library, there are three sequences each with a different repressor binding affinity. The choice of the operator should give a relative fine-tuning of promoter sensitivity to the repressor. In this part, it is explained how we designed the operator libraries and isolated single operators to clone them in the standard format. Moreover, we built and tested: a LacI regulated promoter to tune promoter activation and a lexA based promoter to study the SOS activation (UV and hydrogen peroxide). So wet!