Disruption of MRG19 results in altered nitrogen metabolic status and defective pseudohyphal development in Saccharomyces cerevisiae

Abstract

It was previously shown that MRG19 downregulates carbon metabolism in Saccharomyces cerevisiae upon glucose exhaustion, and that the gene is glucose repressed. Here, it is shown that glucose repression of MRG19 is overcome upon nitrogen withdrawal, suggesting that MRG19 is a regulator of carbon and nitrogen metabolism. b-Galactosidase activity fostered by the promoter of GDH1/3, which encode anabolic enzymes of nitrogen metabolism, was altered in an MRG19 disruptant. As compared to the wild-type strain, the MRG19 disruptant showed a decrease in the ratio of 2-oxoglutarate to glutamate under nitrogen-limited conditions. MRG19 disruptants showed reduced pseudohyphal formation and enhanced sporulation, a phenomenon that occurs under conditions of both nitrogen and carbon withdrawal. These studies revealed that MRG19 regulates carbon and nitrogen metabolism, as well as morphogenetic changes, suggesting that MRG19 is a component of the link between the metabolic status of the cell and the corresponding developmental pathway. INTRODUCTIONMicro-organisms are endowed with the genetic capability to respond to frequently changing carbon and/or nitrogen deprivation by undergoing unique developmental changes. In Saccharomyces cerevisiae, deprivation of carbon and/or nitrogen elicits changes in metabolism and development to circumvent the nutritional deprivation (Esposito & Klapholz, 1981;Werner-Washburne et al., 1996;Gancedo, 2001). Diploid cells of S. cerevisiae undergo sporulation when carbon and nitrogen supply is limited (Esposito & Klapholz, 1981), whereas they put forth pseudohyphae in the absence of nitrogen but in the presence of glucose (Lorenz et al., 2000). These developmental changes, which are due to a combination of signals occurring in response to carbon and nitrogen withdrawal, indicate that the regulation of carbon and nitrogen metabolism is in some way interconnected. GLN3 responds to the low-nitrogen signal, and activates the transcription of nitrogen cataboliterepressed genes (Cunningham et al., 1996); mutation in this gene leads to an inability to put forth pseudohyphae (Lorenz & Heitman, 1998a, b). Recently, it was shown that GLN3 is also regulated by the glucose-responsive SNF1-kinase-mediated phosphorylation mechanism (Bertram et al., 2002;Cox et al., 2002); thus, it is evident that the regulation of carbon and nitrogen metabolism is interdependent. While it is clear that a unique collection of metabolic signals are required to induce specific morphogenetic changes, the underlying metabolic basis that predisposes the cell to opt for one or the other developmental programme is not clear.MRG19 was isolated as a multi-copy repressor of galactose toxicity (Kabir et al., 2000). It was observed that disruption of MRG19 resulted in the derepression of CYC1 under conditions of carbon limitation (Khanday et al., 2002). Based on this, it was suggested that in a wild-type strain, the function of MRG19 is to regulate the oxidation of limited carbon so as to channel it for biosynthesis. The protein is localized i...

Mrg19 depletion increases S. cerevisiae lifespan by augmenting ROS defence

“…Abbreviations: CR, caloric restriction; ROS, reactive oxygen species; DCFDA, dichloro fluorescein di acetate Mrg19 is a putative transcription factor that regulates carbon and nitrogen metabolism by acting as a potential repressor of CYC1 promoter [12]. CYC1 gene is involved in electron flow through the mitochondria under aerobic condition.…”

Plasma membrane localization of paralogous leucine permeases Bap2 and Bap3 is regulated by Bul1

“…Our lab has been investigating the role of MRG19 (aka CSR2, ART8) in carbon and nitrogen metabolism (Kabir et al, 2000;Khanday et al, 2002;Das & Bhat, 2005). A mrg19∆ strain grew better than its WT (wild type) colleague, when branched chain amino acids were used as nitrogen sources (Das., 2005).…”

The efficiency of mitochondrial electron transport chain is increased in the long‐lived mrg19 Saccharomyces cerevisiae

“…, 2005). Mrg19p has been reported to be a putative transcription factor responsible for the utilization of carbon and nitrogen sources (Das & Bhat, 2005; Khanday et al , 2002). However, recent studies (Lin et al.…”