Glutamine transport as a possible regulator of nitrogen catabolite repression in Saccharomyces cerevisiae

Nitrogen catabolite repression (NCR) is a major transcriptional control pathway governing nitrogen use in yeast, with several hundred of target genes identified to date. Early and extensive studies on NCR led to the identification of the 4 GATA zinc finger transcription factors, but the primary mechanism initiating NCR is still unclear up till now. To identify novel players of NCR, we have undertaken a genetic screen in an NCR-relieved gdh1 Delta mutant, which led to the identification of four genes directly linked to protein ubiquitylation. Ubiquitylation is an important way of regulating amino acid transporters and our observations being specifically observed in glutamine-containing media, we hypothesized that glutamine transport could be involved in establishing NCR. Stabilization of Gap1 at the plasma membrane restored NCR in gdh1 Delta cells and AGP1 (but not GAP1) deletion could relieve repression in the ubiquitylation mutants isolated during the screen. Altogether, our results suggest that deregulated glutamine transporter function in all three weak nitrogen derepressed (wnd) mutants restores the repression of NCR-sensitive genes consecutive to GDH1 deletion.

Automated summary

Nitrogen catabolite repression (NCR) is a major transcriptional control pathway governing nitrogen use in yeast. In this study, a genetic screen identified four genes directly linked to protein ubiquitylation, which plays an important role in regulating amino acid transporters. Glutamine transport was found to potentially be involved in establishing NCR. Overall, deregulated glutamine transporter function could restore the repression of NCR-sensitive genes in mutants with a deleted GDH1 gene.