Repressor
Repressor as is known in the genetics a protein which binds to the operator in the DNA, thereby blocking the binding of RNA polymerase to the promoter. Wherein transcription of a gene located in the operon is inhibited. As a result, no mRNA is produced here, which could often result in the translation of the encoded proteins to form enzymes. This remains under the expression of the genes blocked. The effect of the repressor can be regulated by various factors.
The repressor itself is encoded by a regulator gene.
Does the repressor only be activated by a suitable co - repressor, it is called aporepressor. If the aporepressor is activated by the end product of a chain reaction, one speaks of the end product repression.
An inductor, however, changed the repressor so that it releases from the operator and hence gene expression is activated.
Mechanisms
Repressors play an important role in gene regulation:
- In the substrate in the course of induction of the catabolite repression, the substrate encoded by the structural enzyme acts as an inducer to the repressor, which is thus deactivated, and thus makes the expression of the enzyme and the possible degradation of the substrate (for example, lactose operon of E. coli).
- The attenuation of the tryptophan synthesis in prokaryotic (eg E. coli) is blocked by a trp repressor, which contains tryptophan as a co-repressor. The aporepressor ( without bound tryptophan) can not block transcription of the tryptophan operon.