Probably acts as a repressor of iacA expression. Exposure to indole-3-acetic acid (IAA) probably relieves the repressor activity. Induced in the presence of IAA. Transformation of P.putida KT2440, which cannot degrade IAA, with the iac gene cluster confers the ability to grow on IAA as a sole source of carbon and energy, but not the ability to chemotaxis towards IAA.