The Attorney General shall give the district attorneys of the several circuits any opinion, instruction or advice necessary or proper to aid them in the proper discharge of their duties, either by circular or personal letter, and may direct any district attorney to aid and assist in the investigation or prosecution of any case in which the state is interested, in any other circuit than that of the district attorney so directed. Such district attorney shall have and exercise in such other circuit all the powers and authority imposed by law upon the district attorney of such other circuit, but this section shall not abridge any authority which may have been or which may be vested in the Chief Justice of the Supreme Court, nor shall the Attorney General, or any assistant of the Attorney General, or other person at the instance or request of the Attorney General, be authorized to appear or in any way act in the name of the state in civil action or proceeding by or against any county or county officer in which the State of Alabama has no direct financial interest.