The Commissioner of Revenue, with the approval of the Attorney General, shall be authorized, subject to the provisions of the Merit System law, to appoint not more than 15 assistant counsel as may be necessary to transact the legal business of the Department of Revenue. Each such assistant counsel shall be at least 25 years of age, shall have the other qualifications and duties of the legal counsel, shall be commissioned as an Assistant Attorney General and take the oath required of other assistant attorneys general, and shall have the authority and duties of an Assistant Attorney General.