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| Modern Genetic Analysis Chapter 14. Regulation of Gene Transcription Regulation of the Lactose System Figure 14-5. Regulation of the lac operon. The I gene continually makes repressor. The repressor binds to the O (operator) region, blocking the RNA polymerase bound to P (the promoter region) from transcribing the adjacent structural genes. When lactose is present, it binds to the repressor and changes its shape so that the repressor no longer binds to O. The RNA polymerase is then able to transcribe the Z, Y, and A structural genes, so the three enzymes are produced.

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