Question

Co-repressor binds with:
(A) Promoter gene
(B) Operator gene
(C) Aporepressor
(D) Regulator gene

Answer 1

Hint: The activating ligand of a repressor protein is referred to as a corepressor in prokaryotes. For instance, the tryptophan repressor (TrpR) in E. coli can only bind to DNA and inhibit the transcription of the trp operon when tryptophan, its corepressor, is attached to it.

Complete Step by Step Answer:
In order to create the repressor co-repressor complex, the negative operon co-repressor must first bind to the repressor, which then binds to the operator. It is known as a negative control system because the regulator's end product, the repressor, works by preventing the transcription of structural genes. LacZ, LacY, and LacA are the three coding regions that make up the lac operon. The lacZ gene produces the -galactosidase enzyme that breaks down lactose. Lactose is transported into cells via the lacY gene product, lactose permease, while the lacA gene product, lactose acetylase, performs an unidentified and typically optional function. When glucose is available in abundance, the regulator gene creates a repressor also known as an aporepressor, which suppresses the lac operon. The operator gene is blocked by aporepressor. Due to Allolactose's inability to interact with a repressor, the lac operon is turned off and the transcription process is suppressed. This shape shift enables the repressor to bind to the operator and prevent transcription in the case of a corepressor (such as tryptophan). A repressor separates from the operator when an inducer is present, enabling transcription to start.
So, option (C) is the correct answer.

Note: A protein called a repressor prevents the expression of genes. A protein called a corepressor binds to transcription factors and thereby indirectly controls the expression of genes. Corepressor complexes are attracted by repressors.