Affiliation:
1. Department of Genetics, The University of Melbourne, Victoria 3010, Australia
Abstract
ABSTRACT
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.
Publisher
American Society for Microbiology
Subject
Molecular Biology,General Medicine,Microbiology
Cited by
35 articles.
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