Final answer:
The ArgR repressor requires the corepressor arginine to adopt a conformation that can bind to the DNA operator. This is an example of gene regulation, which ensures efficient use of cellular resources by controlling gene expression based on metabolic needs.
Step-by-step explanation:
The arginine repressor ArgR requires the presence of its corepressor arginine in order to bind to DNA effectively. The reason for this requirement is related to the allosteric effect of arginine on the ArgR protein. When arginine is not present, ArgR does not adopt the necessary conformation to interact with the DNA sequence at the operator. In the presence of arginine, the protein changes its shape in such a way that it can now bind to the operator sequence, much like the tryptophan repressor does in the presence of tryptophan.
This mechanism is a fine example of gene regulation wherein the cell economizes resources. Gene expression is tightly controlled to occur only when required, as synthesizing proteins necessitates the use of energy and materials. This is efficient for the cell since it prevents wasting resources on producing proteins, like those for arginine or lactose digestion, when they are not needed, thereby conserving energy.