Abstract

The amdS gene of A. nidulans has proved extremely favourable for the isolation of mutations affecting gene regulation. Trans‐acting regulatory genes involved in amdS induction by small molecular weight effectors have been identified – amdR (ω‐amino acids) facB (acetate) and amdA (acetate). Another gene, the areA gene, has properties expected of a major activator gene involved in nitrogen metabolite repression of amdS. All of these regulatory genes are also involved in the control of various other functions encoded by structural genes unlinked to amdS. Mutations in the 5′‐region adjacent to amdS have been isolated and allow the identification of independent cis‐acting sequences which are the target sites for the regulatory genes. The involvement of these sequences in regulatory product binding has been deduced from titration studies using transformants containing multiple copies of the 5′ sequences. A combination of genetics and molecular analysis is allowing a detailed characterization of this system.