Repression
This is a negative repressive feedback mechanism. The repressor for the trp operon is produced upstream by the trpR gene, which is continually expressed at a low level. It creates monomers, which associate into tetramers. These tetramers are inactive and are dissolved in the nucleoplasm. When tryptophan is present, these tryptophan repressor tetramers bind to tryptophan, causing a change in conformation (in the repressor), which allows the repressor to bind the operator. This prevents RNA polymerase from binding to and transcribing the operon, so tryptophan is not produced from its precursor. When tryptophan is not present, the repressor is in its inactive conformation and cannot bind the operator region, so transcription is not inhibited by the repressor.
Read more about this topic: Trp Operon
Famous quotes containing the word repression:
“Since the death instinct exists in the heart of everything that lives, since we suffer from trying to repress it, since everything that lives longs for rest, let us unfasten the ties that bind us to life, let us cultivate our death wish, let us develop it, water it like a plant, let it grow unhindered. Suffering and fear are born from the repression of the death wish.”
—Eugène Ionesco (b. 1912)
“People with a culture of poverty suffer much less from repression than we of the middle class suffer and indeed, if I may make the suggestion with due qualification, they often have a hell of a lot more fun than we have.”
—Brian Friel (b. 1929)
“Despots play their part in the works of thinkers. Fettered words are terrible words. The writer doubles and trebles the power of his writing when a ruler imposes silence on the people. Something emerges from that enforced silence, a mysterious fullness which filters through and becomes steely in the thought. Repression in history leads to conciseness in the historian, and the rocklike hardness of much celebrated prose is due to the tempering of the tyrant.”
—Victor Hugo (1802–1885)