Subject to applicable rules of the State Merit System of Personnel Administration, the Department of Administrative Services may appoint as many assistants and employees, and fix their salaries, as are essential to the state's interest in the execution of the terms and provisions of this part. Assignment of an assistant or assistants to any of the departments, institutions, or agencies of the state may be made by the Department of Administrative Services. It shall be unlawful for any other agency of the state to employ any person for the purposes set out in this part.