An operon in E. coli is controlled by a repressor that binds at two operator sites (O1 and O2). In the presence of the appropriate inducer, a transcription rate of 100 is observed, but in the absence of inducer, the transcription rate falls to 5. If either of the two sites is mutated so that the repressor cannot bind, then the transcription rate is observed to be 100. Additionally, if base pairs are inserted between the two operator sites, the level of transcription is found to vary with the size of the insert. Briefly explain this data.