Nitrogen regulation in fungi.

Nitrogen regulation has been extensively studied in fungi revealing a complex array of interacting regulatory genes. The general characterisation of the systems in Aspergillus nidulans and Neurospora crassa shall be briefly described, but much of this paper will concentrate specifically on the recent molecular characterisation of areA, the principle regulatory gene from A. nidulans which mediates nitrogen metabolite repression. Three areas shall be explored in detail, firstly the DNA binding domain, which has been characterised extensively by both molecular and genetic analysis. Secondly we shall report recent analysis which has revealed the presence of related DNA binding activities in A. nidulans. Finally we shall discuss the mechanism by which the nitrogen state of the cell is monitored by the areA product, in particular localisation of the domain within the areA product which mediates the regulatory response within the protein.