Identification of functional regions of the positively acting regulatory gene amdR from Aspergillus nidulans

The amdR (intA) regulatory gene of Aspergillus nidulans encodes a 765-amino-acid polypeptide which determines the omega-amino acid induction of at least five structural genes. The AmdR polypeptide contains a potential Zn(II)2Cys6 DNA-binding motif which has been shown to be present in the N-terminal region of a large number of fungal activator proteins. In vitro mutagenesis of the fourth cysteine of this motif abolishes AmdR function as shown by loss of complementation of an amdR- mutation and by the AmdR- phenotype of a mutant gene replacement strain. Studies using constructs in which the proposed AmdR DNA-binding motif is replaced with that from another activator, FacB, shows that induction is independent of DNA-binding specificity and that sequences in the C-terminal region of AmdR are activation domains. Sequencing of several amdR mutant alleles which affect activation and/or induction, together with studies of deletion constructs indicate that changes in the conformation of the protein determines its activity and that this is modulated by inducers.