The tamA protein fused to a DNA-binding domain can recruit AreA, the major nitrogen regulatory protein, to activate gene expression in Aspergillus nidulans

Abstract

The area gene of Aspergillus nidulans encodes a GATA zinc finger transcription factor that activates the expression of a large number of genes subject to nitrogen metabolite repression. The amount and activity of the AreA protein under different nitrogen conditions is modulated by transcriptional, post-transcriptional, and post-translational controls. One of these controls of AreA activity has been proposed to involve the NmrA protein interacting with the DNA-binding domain and the extreme C terminus of AreA to inhibit DNA binding under nitrogen sufficient conditions. In contrast, mutational evidence suggests that the tamA gene has a positive role together with area in regulating the expression of genes subject to nitrogen metabolite repression. This gene was identified by the selection of mutants resistant to toxic nitrogen source analogues, and a number of nitrogen metabolic activities have been shown to be reduced in these mutants. To investigate the role of this gene we have used constructs encoding the TamA protein fused to the DNA-binding domain of either the FacB or the AmdR regulatory proteins. These hybrid proteins have been shown to activate expression of the genes of acetate or GABA utilization, respectively, as well as the amdS gene. Strong activation was shown to require the ArcA protein but was not dependent on Area binding to DNA. The homologous areA gene of A. oryzae and nit-2 gene of Neurospora crassa can substitute for A. nidulans areA in this interaction. We have shown that the same C-terminal region of AreA and NIT-2 that is involved in the interaction with NmrA is required for the TamA-AreA interaction. However, it is unlikely that TamA requires the same residues as NmrA within the GATA DNA-binding domain of AreA.