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This operon is an example of repressible negative regulation of gene expression. The repressor protein binds to the operator in the presence of tryptophan (repressing transcription ) and is released from the operon when tryptophan is absent (allowing transcription to proceed).
For example, the E. coli tryptophan repressor (TrpR) is only able to bind to DNA and repress transcription of the trp operon when its corepressor tryptophan is bound to it. TrpR in the absence of tryptophan is known as an aporepressor and is inactive in repressing gene transcription. [2]
The trp operon, involved in the synthesis of tryptophan (which itself acts as the corepressor), is a negatively controlled repressible operon. Operons can also be positively controlled. With positive control, an activator protein stimulates transcription by binding to DNA (usually at a site other than the operator).
The gal operon is a prokaryotic operon, which encodes enzymes necessary for galactose metabolism. [1] Repression of gene expression for this operon works via binding of repressor molecules to two operators. These repressors dimerize, creating a loop in the DNA.
Enzyme induction is a process in which a molecule (e.g., a drug) induces (i.e., initiates or enhances) the expression of an enzyme. The induction of heat shock proteins in the fruit fly Drosophila melanogaster. The Lac operon is an interesting example of how gene expression can be regulated.
The trp operon consists of a regulatory gene, a promoter, an operator, and a terminator. The trp operon is active only when cellular tryptophan is scarce. If there isn't enough tryptophan, the repressor protein breaks off from the operator (where the repressor is normally bound) and RNA polymerase can complete its reading of the strand of DNA ...
The lacZYA operon houses genes encoding proteins needed for lactose breakdown. [2] The lacI gene codes for a protein called "the repressor" or "the lac repressor", which functions to repressor of the lac operon. [2] The gene lacI is situated immediately upstream of lacZYA but is transcribed from a lacI promoter. [2]
These enzymes can add or remove covalent modifications such as methyl groups, acetyl groups, phosphates, and ubiquitin. Histone modifications serve to recruit other proteins which can either increase the compaction of the chromatin and sequester promoter elements, or to increase the spacing between histones and allow the association of ...