Step 5: With the active repressor protein bound to the Operator region, RNA polymerase (the enzyme responsible for the transcription of genes) is unable to bind to the Promoter region of the trp operon.
Step 6: If RNA polymerase does not bind to the Promoter region, the five trp operon structural genes are not transcribed into mRNA.
Step 7: Without the transcription of the five genes, the five enzymes needed for the bacterium to synthesize the amino acid tryptophan are not made.

Illustration of Function of A Repressible Operon in the Presence of a Corepressor
(The Tryptophan Operon).jpg by Gary E. Kaiser, Ph.D. Professor of Microbiology, The Community College of Baltimore County, Catonsville Campus
This work is licensed under a Creative Commons Attribution 4.0 International License.
Based on a work at https://cwoer.ccbcmd.edu/science/microbiology/index_gos.html.

Last updated: August, 2018
Please send comments and inquiries to Dr. Gary Kaiser