title: The role of nitrate reductase in the regulation of the nitrate assimilation pathway in the yeast Hansenula polymorpha.
abstract: The role of nitrate reductase (NR) in the regulation of the nitrate assimilation pathway was evaluated in the yeast Hansenula polymorpha. Posttranscriptional regulation of NR in response to reduced nitrogen sources and the effect of a heterologous NR on the transcriptional regulation of nitrate-assimilatory gene expression was examined. The strain bearing YNR1 (nitrate reductase gene) under the control of the methanol-induced MOX (methanol oxidase) promoter showed that NR is active in the presence of reduced nitrogen sources. In cells incubated with glutamine plus nitrate, rapamycin abolished nitrogen catabolite repression, NR activity being very similar to that in cells induced by nitrate alone. This reveals the involvement of the Tor-signalling pathway in the transcriptional regulation of H. polymorpha nitrate assimilation genes. To assess the role of NR in nitrate-assimilatory gene expression, different strains lacking YNR1, or both YNR1 and YNT1 (high-affinity nitrate transporter) genes, or expressing the tobacco NR under the YNR1 promoter, were used. Tobacco NR abolished the constitutive nitrate-assimilatory gene induction shown by an NR gene disruptant strain. Moreover, in strains lacking the high-affinity nitrate transporter and NR this deregulation disappeared. These facts discard the role of NR protein in the transcriptional induction of the nitrate-assimilatory genes and point out the involvement of the high-affinity nitrate transporter as a part of the nitrate-signalling pathway.
authors: Departamento de Bioquímica y Biología Molecular, Grupo del Metabolismo del Nitrógeno, Universidad de La Laguna, E-38206 La Laguna, Canarias, Tenerife, Spain.
authors: Francisco J
authors: FJ
authors: Navarro
authors: Germán
authors: G
authors: Perdomo
authors: Paula
authors: P
authors: Tejera
authors: Braulio
authors: B
authors: Medina
authors: Félix
authors: F
authors: Machín
authors: Rosa Maria
authors: RM
authors: Guillén
authors: Ana
authors: A
authors: Lancha
authors: José M
authors: JM
authors: Siverio
mesh_terms: D000935:Antifungal Agents / Q000494:pharmacology; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism*; D015966:Gene Expression Regulation, Fungal / Q000187:drug effects; D005800:Genes, Fungal; D009565:Nitrate Reductases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D009566:Nitrates / Q000378:metabolism*; D010843:Pichia / Q000201:enzymology* / Q000235:genetics; D000644:Quaternary Ammonium Compounds / Q000378:metabolism; D020123:Sirolimus / Q000494:pharmacology; D014026:Nicotiana; D015533:Transcriptional Activation; D014162:Transfection
chemical_list: D000935:Antifungal Agents; D002352:Carrier Proteins; D005656:Fungal Proteins; D009566:Nitrates; D000644:Quaternary Ammonium Compounds; D009565:Nitrate Reductases; D020123:Sirolimus