When tryptophan is limited, there is a slow translation of the early trp leader mRNA which enables domain 2 to pair with domain 3 and form an antiterminator loop. Transcription of the remainder of the trp operon continues and the enzymes required for tryptophan synthesis are made. Slow initial translation is able to occur with low levels of tryptophan present because there is limited Trp tRNA available to translate the two Trp codons (asterisks) causing the ribosome to stall at the Trp codons and enabling domain 2 to pair with domain 3 rather than domain 1.

Illustration of Attenuation in the Trp Operon of Escherichia coli: Low Levels of Tryptophan.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