Abstract
Nitrogen catabolite repression (NCR) is the regulatory pathway through which Saccharomyces cerevisiae responds to the available nitrogen status and selectively utilizes rich nitrogen sources in preference to poor ones. Expression of NCR-sensitive genes is mediated by two transcription activators, Gln3 and Gat1, in response to provision of a poorly used nitrogen source or following treatment with the TORC1 inhibitor, rapamycin. During nitrogen excess, the transcription activators are sequestered in the cytoplasm in a Ure2-dependent fashion. Here, we show that Vps components are required for Gln3 localization and function in response to rapamycin treatment when cells are grown in defined yeast nitrogen base but not in complex yeast peptone dextrose medium. On the other hand, Gat1 function was altered in vps mutants in all conditions tested. A significant fraction of Gat1, like Gln3, is associated with light intracellular membranes. Further, our results are consistent with the possibility that Ure2 might function downstream of the Vps components during the control of GATA factor-mediated gene expression. These observations demonstrate distinct media-dependent requirements of vesicular trafficking components for wild-type responses of GATA factor localization and function. As a result, the current model describing participation of Vps system components in events associated with translocation of Gln3 into the nucleus following rapamycin treatment or growth in nitrogen-poor medium requires modification.
Highlights
Nitrogen is a naturally occurring element that is essential for the growth of all living cells
Gln3 nuclear localization is impaired in response to nitrogen limitation but not rapamycin treatment in yeast peptone dextrose (YPD)-pregrown vps mutants, we show that in yeast nitrogen base (YNB) ammonia, Vps proteins are required for Gln3 nuclear localization even in response to rapamycin
The expression levels exhibited by rapamycin-treated or proline-transferred wild types (WT) cells were clearly impaired in gln3Δ or gat1Δ-mutant cells, demonstrating that DAL5 transcription requires the simultaneous presence of Gln3 and Gat1 when YNBammonia-grown cells are transferred to proline medium, or treated with rapamycin (Georis et al 2008)
Summary
Nitrogen is a naturally occurring element that is essential for the growth of all living cells. Addition of the immunosuppressant drug rapamycin, inhibiting TORC1, to cells growing in the presence of a good nitrogen source transiently mimics the effects observed with a poor one, that is, nuclear localization and activation of NCR gene expression by Gln and Gat (Beck and Hall 1999; Cardenas et al 1999; Hardwick et al 1999). Puria et al (2008) have previously observed a requirement of Class C and D Vps proteins for Gln nuclear translocation after transferring yeast peptone dextrose (YPD) grown cells to proline medium but not after treating them with rapamycin. Our observations suggest that Ure might function downstream the Vps proteins during GATA factor-mediated signaling
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