Repressor
In genetics, a repressor is a protein that binds to the operator in the DNA and thus blocks the binding of the RNA polymerase to the promoter . This prevents the transcription of a gene located within the operon . As a result, no mRNA is produced here that could lead to the formation of the encoded proteins, often enzymes , during translation . Therefore omitted the expression of genes blocked. The action of the repressor can be regulated by various factors.
The repressor itself is encoded by a regulatory gene. If the repressor has to be activated by a suitable corepressor , it is called an aporepressor . If the aporepressor is activated by the end product of a reaction chain, it is called end product repression . An inducer, on the other hand, changes the repressor in such a way that it detaches itself from the operator and thus activates gene expression. This process is also known as derepression .
Mechanisms
Repressors play an important role in gene regulation:
- In the case of substrate induction in the course of catabolite repression, the substrate of the enzyme encoded by the structural gene acts as an inducer on the repressor, which is thus deactivated and thus also enables the expression of the enzyme and the degradation of the substrate (example: lactose operon in E. coli ) .
- The attenuation of tryptophan synthesis in prokaryotes (e.g. E. coli ) is blocked by a trp repressor that contains tryptophan as a corepressor. The aporepressor (without bound tryptophan) can not block the transcription of the tryptophan operon .
literature
- Jeremy M. Berg, John L. Tymoczko, Lubert Stryer: Stryer Biochemie , 6th edition, Spektrum Akademischer Verlag, Munich 2007. ISBN 978-3-8274-1800-5 .
Web links
Individual proof
- ^ Lubert Stryer: Biochemie , 4th edition, Spectrum, Heidelberg, 1996, ISBN 978-3860253465 , p. 1009 f.