title: Opposing signals differentially regulate transcript stability in Aspergillus nidulans.
abstract: A good model for gene regulation, requiring the organism to monitor a complex and changing environment and respond in a precise and rapid way, is nitrogen metabolism in Aspergillus nidulans. This involves co-ordinated expression of hundreds of genes, many dependent on the transcription factor AreA, which monitors the nitrogen state of the cell. AreA activity is in part modulated by differential degradation of its transcript in response to intracellular glutamine. Here we report that glutamine triggers synchronized degradation of a large subset of transcripts involved in nitrogen metabolism. Among these are all four genes involved in the assimilation of nitrate. Significantly, we show that two of these transcripts, niaD and niiA, are stabilized by intracellular nitrate, directly reinforcing transcriptional regulation. Glutamine-signalled degradation and the nitrate-dependent stabilization of the niaD transcript are effected at the level of deadenylation and are dependent on its 3' UTR. When glutamine and nitrate are both present, nitrate stabilization is predominant, ensuring that nitrate and the toxic intermediate nitrite are removed from the cell. Regulated transcript stability is therefore an integral part of the adaptive response. This represents the first example of distinct physiological signals competing to differentially regulate transcripts at the level of deadenylation.
authors.affiliation: The University of Liverpool, School of Biological Sciences, Biosciences Building, Crown Street, Liverpool, L69 7ZB, UK.
authors.forename: Mark X
authors.initials: MX
authors.lastname: Caddick
authors.forename: Meriel G
authors.initials: MG
authors.lastname: Jones
authors.forename: J Martin
authors.initials: JM
authors.lastname: van Tonder
authors.forename: Hélène
authors.initials: H
authors.lastname: Le Cordier
authors.forename: Frank
authors.initials: F
authors.lastname: Narendja
authors.forename: Joseph
authors.initials: J
authors.lastname: Strauss
authors.forename: Igor Y
authors.initials: IY
authors.lastname: Morozov
mesh_terms: D020413:3' Untranslated Regions / Q000235:genetics / Q000378:metabolism; D001233:Aspergillus nidulans / Q000235:genetics* / Q000378:metabolism; D015152:Blotting, Northern; D015966:Gene Expression Regulation, Fungal / Q000187:drug effects / Q000235:genetics*; D005800:Genes, Fungal / Q000235:genetics; D005973:Glutamine / Q000378:metabolism* / Q000494:pharmacology; D009566:Nitrates / Q000378:metabolism* / Q000494:pharmacology; D009572:Nitrite Reductases / Q000235:genetics / Q000378:metabolism; D020871:RNA Stability / Q000187:drug effects; D016914:Ribonuclease H / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction
chemical_list: D020413:3' Untranslated Regions; D009566:Nitrates; D005973:Glutamine; D009572:Nitrite Reductases; D016914:Ribonuclease H