Transduction of the nitrogen signal activating Gln3-mediated transcription is independent of Npr1 kinase and Rsp5-Bul1/2 ubiquitin ligase in Saccharomyces cerevisiae.
Nitrogen Catabolite Repression (NCR) allows the adaptation of yeast cells to the quality of nitrogen supply by inhibiting the transcription of genes encoding proteins involved in transport and degradation of nonpreferred nitrogen sources. In cells using ammonium or glutamine, the GATA transcription factor Gln3 is sequestered in the cytoplasm by Ure2 whereas it enters the nucleus after a shift to a nonpreferred nitrogen source like proline or upon addition of rapamycin, the TOR complex inhibitor. Recently, the Npr1 kinase and the Rsp5, Bul1/2 ubiquitin ligase complex were reported to have antagonistic roles in the nuclear import and Gln3-mediated activation. The Npr1 kinase controls the activity of various permeases including transporters for nitrogen sources that stimulate NCR such as the Mep ammonium transport systems. Combining data from growth tests, Northern blot analysis and Gln3 immunolocalization, we show that the Npr1 kinase is not a direct negative regulator of Gln3-dependent transcription. The derepression of Gln3-activated genes in ammonium-grown npr1 cells results from the reduced uptake of the nitrogen-repressing compound because NCR could be restored in npr1 cells by repairing ammonium-uptake defects through different means. Finally, we show that the impairment of the ubiquitin ligase complex does not prevent induction of NCR genes under nonpreferred nitrogen conditions. The apparent Rsp5-, Bul1/2-dependent Gln3 activation keeps to the cellular status, as it is only observed in cells having left the balanced phase of exponential growth.
Feller
André
A
Institut de Recherches Microbiologiques J-M Wiame, Laboratoire de Microbiologie, Université Libre de Bruxelles, 1070 Brussels, Belgium.
Boeckstaens
Mélanie
M
Marini
Anna Maria
AM
Dubois
Evelyne
E
D021581:Active Transport, Cell Nucleus; D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism*; D001692:Biological Transport; D003600:Cytosol / Q000378:metabolism; D056827:Endosomal Sorting Complexes Required for Transport; D015966:Gene Expression Regulation, Fungal; D009584:Nitrogen / Q000737:chemistry / Q000378:metabolism; D011494:Protein Kinases / Q000378:metabolism*; D012097:Repressor Proteins / Q000378:metabolism / Q000502:physiology*; D012441:Saccharomyces cerevisiae / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism* / Q000502:physiology*; D014157:Transcription Factors / Q000378:metabolism / Q000502:physiology*; D014158:Transcription, Genetic; D043743:Ubiquitin-Protein Ligase Complexes / Q000378:metabolism*; D044767:Ubiquitin-Protein Ligases
D048868:Adaptor Proteins, Signal Transducing; C099939:BUL1 protein, S cerevisiae; C117205:BUL2 protein, S cerevisiae; D056827:Endosomal Sorting Complexes Required for Transport; C071664:GLN3 protein, S cerevisiae; D012097:Repressor Proteins; D029701:Saccharomyces cerevisiae Proteins; D014157:Transcription Factors; C066958:NPR1 protein, S cerevisiae; D043743:Ubiquitin-Protein Ligase Complexes; D044767:Ubiquitin-Protein Ligases; D011494:Protein Kinases; C469287:RSP5 protein, S cerevisiae; D009584:Nitrogen