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Eukaryotic Cell, February 2006, p. 226-237, Vol. 5, No. 2
1535-9778/06/$08.00+0     doi:10.1128/EC.5.2.226-237.2006
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

Differential Expression of Aspergillus nidulans Ammonium Permease Genes Is Regulated by GATA Transcription Factor AreA

Brendon J. Monahan,{dagger} Marion C. Askin, Michael J. Hynes, and Meryl A. Davis*

Department of Genetics, The University of Melbourne, Victoria 3010, Australia

Received 21 August 2005/ Accepted 14 November 2005

The movement of ammonium across biological membranes is mediated in both prokaryotes and eukaryotes by ammonium transport proteins (AMT/MEP) that constitute a family of related sequences. We have previously identified two ammonium permeases in Aspergillus nidulans, encoded by the meaA and mepA genes. Here we show that meaA is expressed in the presence of ammonium, consistent with the function of MeaA as the main ammonium transporter required for optimal growth on ammonium as a nitrogen source. In contrast, mepA, which encodes a high-affinity ammonium permease, is expressed only under nitrogen-limiting or starvation conditions. We have identified two additional AMT/MEP-like genes in A. nidulans, namely, mepB, which encodes a second high-affinity ammonium transporter expressed only in response to complete nitrogen starvation, and mepC, which is expressed at low levels under all nitrogen conditions. The MepC gene product is more divergent than the other A. nidulans AMT/MEP proteins and is not thought to significantly contribute to ammonium uptake under normal conditions. Remarkably, the expression of each AMT/MEP gene under all nitrogen conditions is regulated by the global nitrogen regulatory GATA factor AreA. Therefore, AreA is also active under nitrogen-sufficient conditions, along with its established role as a transcriptional activator in response to nitrogen limitation.

* Corresponding author. Mailing address: Department of Genetics, The University of Melbourne, Victoria 3010, Australia. Phone: (61) (3) 8344 5140. Fax: (61) (3) 8344 5139. E-mail: m.davis{at}unimelb.edu.au.

{dagger} Present address: Department of Genetics, Harvard Medical School, Boston, MA 02115.

Eukaryotic Cell, February 2006, p. 226-237, Vol. 5, No. 2
1535-9778/06/$08.00+0     doi:10.1128/EC.5.2.226-237.2006
Copyright © 2006, American Society for Microbiology. All Rights Reserved.



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