In e. coli, eight enzymatic steps are involved in the biosynthesis of arginine from glutamate. the synthesis of the required enzymes is subject to control by the argd protein, which, on its own, binds weakly to a regulatory sequence just downstream of the promoter regions for these genes. upon the addition of excess arginine to the growth medium, the respective mrna molecules are no longer produced. what is the likely role of arginine in the control of these genes

Arginine functions as a corepressor in controlling these genes. This is due to the fact that when arginine combines with the ArgD protein it results in the high affinity of ArgD protein for the operator region. Thus, because of which the expression of the gene gets diminished.  

The enzyme that is taking part in the production of arginine from glutamate is also possible to get influenced by the feedback inhibition. As feedback inhibition occurs, it signifies that the product itself mediates the enzymatic activity. Thus, the biosynthesis of arginine from glutamate is monitored by both posts transcriptional as well as transcriptional procedures.