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Recent Advances in Nitrogen Regulation: a Comparison between Saccharomyces cerevisiae and Filamentous Fungi

2008; American Society for Microbiology; Volume: 7; Issue: 6 Linguagem: Inglês

10.1128/ec.00076-08

1535-9778

Koon Ho Wong, Michael J. Hynes, Meryl A. Davis,

Fungal Biology and Applications

Myriad biological processes are dynamically regulated in response to environmental cues.Transcriptional gene regulation is of fundamental importance, and regulatory mechanisms ensure that genes are expressed at levels appropriate to the cellular state.Microorganisms undergo major shifts in their transcriptional profile in response to changes in the nutrients that are available.In the free-living fungi this is evident when different growth substrates are available or when pathogenic species infect their hosts.Three model ascomycetes in particular, Aspergillus nidulans, Neurospora crassa, and Saccharomyces cerevisiae, have contributed much to the detailed functional analysis of metabolic gene regulation due to their small haploid genome size, excellent genetics, and metabolic versatility.Phylogenetic analysis indicates that the filamentous ascomycetes A. nidulans and N. crassa and the hemiascomycete S. cerevisiae belong to separate lineages within Ascomycota (39), which also includes various human and plant pathogens and species with important industrial applications.The increasing availability of fungal genome sequences has enabled comparative studies across species occupying different ecological niches.Nitrogen is an essential requirement for growth, and fungi are able to use a wide variety of compounds as nitrogen sources.However, the use of different nitrogen compounds is selective, and readily assimilated nitrogen sources such as ammonium and glutamine are preferentially used.Underlying this selective utilization of nitrogen sources are complex controls that operate primarily at the transcriptional level.The global regulation of nitrogen source utilization, known as nitrogen catabolite repression (NCR) in S. cerevisiae and nitrogen metabolite repression (NMR) in A. nidulans and N. crassa, involves the regulation of the synthesis of appropriate catabolic enzymes and permeases in response to the nitrogen status of the cell.For many nitrogen sources, expression of the respective catabolic activities is also subjected to pathway-specific control in response to specific inducers (for reviews see references 12, 23, and 65).The major transcription factors regulating nitrogen gene expression in all fungal species studied thus far are GATA factors.These transcription factors share a common DNA