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crnA encodes a nitrate transporter in Aspergillus nidulans
S E Unkles1, K L Hawker, C Grieve
1Plant Molecular Genetics Unit, University of St. Andrews, Fife, Scotland, United Kingdom.
Summary
The Aspergillus nidulans crnA gene encodes a novel nitrate transporter. Its expression is tightly regulated by nitrogen availability at the transcriptional level, involving key regulatory genes.
Area of Science:
- Molecular Biology
- Mycology
- Biochemistry
Background:
- Nitrate transport is crucial for fungal growth and nitrogen assimilation.
- Understanding the molecular mechanisms of nitrate uptake is essential for fungal physiology.
Purpose of the Study:
- To determine the nucleotide sequence of the Aspergillus nidulans crnA gene.
- To characterize the predicted protein structure and regulatory mechanisms of nitrate transport.
Main Methods:
- Nucleotide sequencing of the crnA gene.
- Hydropathy plot analysis for protein structure prediction.
- Northern blotting to analyze gene expression patterns.
- Mutant analysis of regulatory genes (nirA, areA) and nitrate reductase gene (niaD).
Main Results:
- The crnA gene encodes a predicted 483-amino acid polypeptide with 10 membrane-spanning helices.
- The crnA transporter shows no significant homology to known membrane proteins, suggesting a novel class.
- crnA expression is induced by nitrate/nitrite and repressed by nitrogen metabolites at the mRNA level.
- Regulation involves nirA, areA, and niaD gene products.
Conclusions:
- The crnA gene product represents a new family of membrane transporters.
- Nitrate transport in A. nidulans is under complex transcriptional regulation influenced by nitrogen status.
- The study elucidates the genetic control of nitrate assimilation in fungi.