Step 5: Since the inactive repressor protein is unable to bind to the Operator region, RNA polymerase (the enzyme responsible for the transcription of genes) is now able to bind to the Promoter region of the lac operon.
Step 6: RNA polymerase is now able to transcribe the three lac operon structural genes (lacZ, lacY, and lacA) into mRNA.
Step 7: With the transcription of these genes, the enzymes needed for the bacterium to utilize the sugar lactose are now synthesized.

The lacZ gene codes for LacZ (beta-galactosidase), an enzyme that breaks down lactose into glucose and galactose. The lacY gene codes for LacY (beta-galactosidase permease), an enzyme which transports lactose into the bacterium. The lacA gene codes for LacA (transacetylase), of uncertain function in lactose catabolism.

Illustration of An Inducible Operon in the Presence of an Inducer (The Escherichia coli Lactose 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: September, 2018
Please send comments and inquiries to Dr. Gary Kaiser