The @M03958@ by which the synthesis of an enzyme is prevented by @R05304@ molecules. In many cases, the end product of a synthesis chain (e.g. an amino acid) acts as a feed-back corepressor by combining with an intracellular aporepressor protein, so that this complex is able to @B00682@ the function of an operator. As a result, the whole @O04301@ is prevented from being transcribed into mRNA, and the expression of all @E02159@ necessary for the synthesis of the end product amino acid is abolished.