Answer :
In regulation by repression "an amino acid activates the repressor so that the repressor binds to the operator and prevents transcription".
Option: B
Explanation:
A repressor refers RNA- or DNA inbuilt protein which impedes more than one gene transcription when inbuilt to an operator or related silencer in molecular genetics. A DNA-binding repressor restricts the RNA polymerase linkage to the promoter, stopping the genes from staying transcribed into messenger(mRNA).
An RNA-binding repressor binds to mRNA and prevents the mRNA from being converted into protein. This blockage of speech is known as repression. In this, a protein entity called a repressor inhibits the production of an enzyme by binding and thus blocking the function of deoxyribonucleic acid, which regulates the mechanism by which the enzyme is synthesized.