The Yeast GATA Factor Gat1 Occupies a Central Position in Nitrogen Catabolite Repression-Sensitive Gene Activation

Abstract

Saccharomyces cerevisiae cells are able to adapt their metabolism according to the quality of the nitrogen sources available in the environment. Nitrogen catabolite repression (NCR) restrains the yeast's capacity to use poor nitrogen sources when rich ones are available. NCR-sensitive expression is modulated by the synchronized action of four DNA-binding GATA factors. Although the first identified GATA factor, Gln3, was considered the major activator of NCR-sensitive gene expression, our work positions Gat1 as a key factor for the integrated control of NCR in yeast for the following reasons: (i) Gat1 appeared to be the limiting factor for NCR gene expression, (ii) GAT1 expression was regulated by the four GATA factors in response to nitrogen availability, (iii) the two negative GATA factors Dal80 and Gzf3 interfered with Gat1 binding to DNA, and (iv) Gln3 binding to some NCR promoters required Gat1. Our study also provides mechanistic insights into the mode of action of the two negative GATA factors. Gzf3 interfered with Gat1 by nuclear sequestration and by competition at its own promoter. Dal80-dependent repression of NCR-sensitive gene expression occurred at three possible levels: Dal80 represses GAT1 expression, it competes with Gat1 for binding, and it directly represses NCR gene transcription.

Distinct Phosphatase Requirements and GATA Factor Responses to Nitrogen Catabolite Repression and Rapamycin Treatment in Saccharomyces cerevisiae

“…(vi) nuclear targeting of Gln3-Myc 13 alone is insufficient for its recruitment to the DAL5 promoter (48). (vii) Gln3-Myc 13 is not uniformly distributed in the cytoplasm of cells grown under repressive conditions but is associated with a cytoplasmic membrane system (49,50). Extending this observation, nuclear Gln3 localization in derepressive conditions was found to require several components that participate in Golgi-to-endosome vesicle transport (51).…”

“…it is greatest with proline as the nitrogen source and least in glutaminegrown cells (47). (v) In the absence of Pph21/22-Tpd3-Cdc55/ Rts1 activity, Gln3-Myc 13 , which is dephosphorylated to the same level as in glutamine-grown, rapamycin-treated wild type cells, remains localized to the cytoplasm (47). (vi) nuclear targeting of Gln3-Myc 13 alone is insufficient for its recruitment to the DAL5 promoter (48).…”

“…induction is high in ammonia-grown cells and undetectable in proline-or glutamate-grown cells (40 -42). (ii) Observable Gln3-Myc 13 phosphorylation levels do not correlate with the quality or quantity of the nitrogen source provided or the intracellular localization of Gln3-Myc 13 , i.e. Gln3-Myc 13 is hyperphosphorylated in nitrogen-starved, proline-grown, or methionine sulfoximine-treated cells but hypophosphorylated in rapamycin-treated cells.…”

“…Work to this point has provided a detailed view of conditions and phosphatase requirements affecting the intracellular localization of Gln3-Myc 13 . Unfortunately, similar information for Gat1 was lacking except for the observations that rapamycin treatment did not demonstrably affect the electrophoretic mobility of Gat1-Myc 13 (44), and rapamycin-induced nuclear Gat1-Myc 13 localization occurred similarly in wild type and sit4⌬ cells (48).…”

Hap2-3-5-Gln3 determine transcriptional activation of GDH1 and ASN1 under repressive nitrogen conditions in the yeast Saccharomyces cerevisiae

“…This does not exclude the possibility of Gln3-assisted recruitment even under non-repressive conditions. In this regard, Gln3-assisted promoter binding has been observed in nitrogen non-repressive conditions, since Gat1 is required to promote Gln3 binding to the GAP1 promoter in proline-grown cultures (Georis et al, 2009), suggesting that even under conditions favouring Gln3 nuclear localization, its promoter-binding capacity is fostered by additional activators. In addition, the auxiliary modulator must have binding sites on the promoter, probably arranged in a precise combinatorial fashion with the cognate Gln3-binding GATAAG elements.…”