Concept
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The trp Operon: A Repressor Operon
The trp operon
The five genes that are needed to synthesize tryptophan in E. coli are located next to each other in the trp operon. When tryptophan is plentiful, two tryptophan molecules bind the repressor protein at the operator sequence. This physically blocks the RNA polymerase from transcribing the tryptophan genes. When tryptophan is absent, the repressor protein does not bind to the operator and the genes are transcribed.
Source
Boundless vets and curates high-quality, openly licensed content from around the Internet. This particular resource used the following sources:
"OpenStax College, Prokaryotic Gene Regulation. October 16, 2013."
http://cnx.org/content/m44535/latest/Figure_16_02_01.jpg
OpenStax CNX
CC BY 3.0.