More than One Way in: Three Gln3 Sequences Required To Relieve Negative Ure2 Regulation and Support Nuclear Gln3 Import in Saccharomyces cerevisiae

Disordered sequences of transcription factors regulate genomic binding by integrating diverse sequence grammars and interaction types

Intrinsically disordered regions (IDRs) guide transcription factors (TFs) to their genomic binding sites, raising the question of how structure-lacking regions encode for complex binding patterns. We investigated this using the TF Gln3, revealing sets of IDR-embedded determinants that direct Gln3 binding to respective groups of functionally related promoters, and enable tuning binding preferences between environmental conditions, phospho-mimicking mutations, and orthologs. Through targeted mutations, we defined the role of short linear motifs (SLiMs) and co-binding TFs (Hap2) in stabilizing Gln3 at respiration-chain promoters, while providing evidence that Gln3 binding at nitrogen-associated promoters is encoded by the IDR amino-acid composition, independent of SLiMs or co-binding TFs. Therefore, despite their apparent simplicity, TF IDRs can direct and regulate complex genomic binding patterns through a combination of SLiM-mediated and composition-encoded interactions.

TorC1 and nitrogen catabolite repression control of integrated GABA shunt and retrograde pathway gene expression

Despite our detailed understanding of how the lower GABA shunt and retrograde genes are regulated, there is a paucity of validated information concerning control of GAD1, the glutamate decarboxylase gene which catalyzes the first reaction of the GABA shunt. Further, integration of glutamate degradation via the GABA shunt has not been investigated. Here, we show that while GAD1 shares a response to rapamycin-inhibition of the TorC1 kinase, it does so independently of the Gln3 and Gat1 NCR-sensitive transcriptional activators that mediate transcription of the lower GABA shunt genes. We also show that GABA shunt gene expression increases dramatically in response to nickel ions. The α-ketoglutarate needed for the GABA shunt to cycle, thereby producing reduced pyridine nucleotides, derives from the retrograde pathway as shown by a similar high increase in the retrograde reporter, CIT2 when nickel is present in the medium. These observations demonstrate high integration of the GABA shunt, retrograde, peroxisomal glyoxylate cycle, and β-oxidation pathways.

Rapamycin enhanced the production of 2-phenylethanol during whole-cell bioconversion by yeast

2-Phenylethanol (2-PE), a higher alcohol with a rose-like odor, has been widely utilized in food, perfume, and beverages. Saccharomyces cerevisiae is one of the most promising microorganisms for the biosynthesis of natural 2-PE. However, the growth of S. cerevisiae is generally inhibited by 2-PE, which makes its production in yeast cell factories challenging. Here, the whole-cell bioconversion was used to avert growth inhibition, leading to an increase in the concentration and productivity of 2-PE. Moreover, rapamycin (Rap) addition further improved the efficiency of 2-PE synthesis. The concentration of 2-PE (2.20 g/L) was 1.68-fold higher than that in the absence of Rap during the whole-cell bioconversion by S. cerevisiae BY4741. RT-qPCR results showed that Rap addition increased the transcription of ARO9, ARO10, ADH2, GAP1, ARO80, GLN3, and GDH2. When the GLN3 was knocked out, the transcriptional levels of the genes were dramatically decreased, and the concentration of 2-PE significantly decreased to 0.21 g/L. The results indicated that Rap enhanced the flux of the Ehrlich pathway, and Gln3 exerted a central role in the regulation of Rap. Furthermore, commercial yeast (S. cerevisiae FY202001) was selected to verify the applicability of Rap. In the presence of Rap, 3.67 g/L 2-PE was obtained by whole-cell bioconversion in flask, which was increased by 9% than that in the absence of Rap. Finally, the 2-PE titer reached 4.93 g/L by whole-cell bioconversion in a 5 L bioreactor, with a yield of 84 mol% from L-phenylalanine and a productivity of 0.103 g/L h, which was far higher than that of the currently reported in S. cerevisiae. These findings provided a new idea for the efficient synthesis of 2-PE. KEY POINTS: • Whole-cell bioconversion was used to produce 2-PE. • The regulation of the Ehrlich pathway by Rap provides a theoretical basis for developing an effective yeast cell factory to produce 2-PE. • The 2-PE productivity of 0.103 g/L h is far higher than that of the currently reported in S. cerevisiae .

Chromatin Regulators Ahc1p and Eaf3p Positively Influence Nitrogen Metabolism in Saccharomyces cerevisiae

There is a complex regulatory network of nitrogen metabolism in Saccharomyces cerevisiae, and many details of this regulatory network have not been revealed. This study explored the global regulation of nitrogen metabolism in S. cerevisiae from an epigenetic perspective. Comparative transcriptome analysis of S. cerevisiae S288C treated with 30 nitrogen sources identified nine chromatin regulators (CRs) that responded significantly to different nitrogen sources. Functional analysis showed that among the CRs identified, Ahc1p and Eaf3p promoted the utilization of non-preferred nitrogen sources through global regulation of nitrogen metabolism. Ahc1p regulated nitrogen metabolism through amino acid transport, nitrogen catabolism repression (NCR), and the Ssy1p-Ptr3p-Ssy5p signaling sensor system. Eaf3p regulated nitrogen metabolism via amino acid transport and NCR. The regulatory mechanisms of the effects of Ahc1p and Eaf3p on nitrogen metabolism depended on the function of their histone acetyltransferase complex ADA and NuA4. These epigenetic findings provided new insights for a deeper understanding of the nitrogen metabolism regulatory network in S. cerevisiae.

Gene co-expression network analysis reveals the positive impact of endocytosis and mitochondria-related genes over nitrogen metabolism in Saccharomyces cerevisiae

Nitrogen metabolism is essential for most cellular activities. Therefore, a deep understanding of its regulatory mechanisms is necessary for the efficient utilization of nitrogen sources for Saccharomyces cerevisiae. In this study, a gene co-expression network was constructed for S. cerevisiae S288C with different nitrogen sources. From this, a key gene co-expression module related to nitrogen source preference utilization was obtained, and 10 hub genes centrally located in the co-expression network were identified. Functional studies verified that the endocytosis-related genes CAP1 and END3 significantly increased the utilization of multiple non-preferred amino acids and reduced the accumulation of the harmful nitrogen metabolite precursor urea by regulating amino acid transporters and TOR pathway. The mitochondria-related gene ATP12, MRPL22, MRP1 and NAM9 significantly increased the utilization of multiple non-preferred amino acids and reduced accumulation of the urea by coordinately regulating nitrogen catabolism repression, Ssy1p-Ptr3p-Ssy5p signaling sensor system, amino acid transporters, TOR pathway and urea metabolism-related pathways. Furthermore, these data revealed the potential positive effects of endocytosis and mitochondrial ribosomes protein translation on nitrogen source preference. This study provides new analytical perspectives for complex regulatory networks involving nitrogen metabolism in S. cerevisiae.

Effects of abolishing Whi2 on the proteome and nitrogen catabolite repression-sensitive protein production

In yeast physiology, a commonly used reference condition for many experiments, including those involving nitrogen catabolite repression (NCR), is growth in synthetic complete (SC) medium. Four SC formulations, SCCSH,1990, SCCSH,1994, SCCSH,2005, and SCME, have been used interchangeably as the nitrogen-rich medium of choice [Cold Spring Harbor Yeast Course Manuals (SCCSH) and a formulation in the methods in enzymology (SCME)]. It has been tacitly presumed that all of these formulations support equivalent responses. However, a recent report concluded that (i) TorC1 activity is downregulated by the lower concentration of primarily leucine in SCME relative to SCCSH. (ii) The Whi2-Psr1/2 complex is responsible for this downregulation. TorC1 is a primary nitrogen-responsive regulator in yeast. Among its downstream targets is control of NCR-sensitive transcription activators Gln3 and Gat1. They in turn control production of catabolic transporters and enzymes needed to scavenge poor nitrogen sources (e.g., Proline) and activate autophagy (ATG14). One of the reporters used in Chen et al. was an NCR-sensitive DAL80-GFP promoter fusion. This intrigued us because we expected minimal if any DAL80 expression in SC medium. Therefore, we investigated the source of the Dal80-GFP production and the proteomes of wild-type and whi2Δ cells cultured in SCCSH and SCME. We found a massive and equivalent reorientation of amino acid biosynthetic proteins in both wild-type and whi2Δ cells even though both media contained high overall concentrations of amino acids. Gcn2 appears to play a significant regulatory role in this reorientation. NCR-sensitive DAL80 expression and overall NCR-sensitive protein production were only marginally affected by the whi2Δ. In contrast, the levels of 58 proteins changed by an absolute value of log2 between 3 and 8 when Whi2 was abolished relative to wild type. Surprisingly, with only two exceptions could those proteins be related in GO analyses, i.e., GO terms associated with carbohydrate metabolism and oxidative stress after shifting a whi2Δ from SCCSH to SCME for 6 h. What was conspicuously missing were proteins related by TorC1- and NCR-associated GO terms.

Target of Rapamycin Complex 1 (TORC1), Protein Kinase A (PKA) and Cytosolic pH Regulate a Transcriptional Circuit for Lipid Droplet Formation

Lipid droplets (LDs) are ubiquitous organelles that fulfill essential roles in response to metabolic cues. The identification of several neutral lipid synthesizing and regulatory protein complexes have propelled significant advance on the mechanisms of LD biogenesis in the endoplasmic reticulum (ER). However, our understanding of signaling networks, especially transcriptional mechanisms, regulating membrane biogenesis is very limited. Here, we show that the nutrient-sensing Target of Rapamycin Complex 1 (TORC1) regulates LD formation at a transcriptional level, by targeting DGA1 expression, in a Sit4-, Mks1-, and Sfp1-dependent manner. We show that cytosolic pH (pHc), co-regulated by the plasma membrane H+-ATPase Pma1 and the vacuolar ATPase (V-ATPase), acts as a second messenger, upstream of protein kinase A (PKA), to adjust the localization and activity of the major transcription factor repressor Opi1, which in turn controls the metabolic switch between phospholipid metabolism and lipid storage. Together, this work delineates hitherto unknown molecular mechanisms that couple nutrient availability and pHc to LD formation through a transcriptional circuit regulated by major signaling transduction pathways.

N- and C-terminal Gln3-Tor1 interaction sites: one acting negatively and the other positively to regulate nuclear Gln3 localization

Gln3 activates Nitrogen Catabolite Repression, NCR-sensitive expression of the genes required for Saccharomyces cerevisiae to scavenge poor nitrogen sources from its environment. The global TorC1 kinase complex negatively regulates nuclear Gln3 localization, interacting with an α-helix in the C-terminal region of Gln3, Gln3656-666. In nitrogen replete conditions, Gln3 is sequestered in the cytoplasm, whereas when TorC1 is down-regulated, in nitrogen restrictive conditions, Gln3 migrates into the nucleus. In this work, we show that the C-terminal Gln3-Tor1 interaction site is required for wild type, rapamycin-elicited, Sit4-dependent nuclear Gln3 localization, but not for its dephosphorylation. In fact, truncated Gln31-384 can enter the nucleus in the absence of Sit4 in both repressive and derepressive growth conditions. However, Gln31-384 can only enter the nucleus if a newly discovered second positively-acting Gln3-Tor1 interaction site remains intact. Importantly, the N- and C-terminal Gln3-Tor1 interaction sites function both autonomously and collaboratively. The N-terminal Gln3-Tor1 interaction site, previously designated Gln3URS contains a predicted α-helix situated within an unstructured coiled-coil region. Eight of the thirteen serine/threonine residues in the Gln3URS are dephosphorylated 3-15-fold with three of them by 10-15-fold. Substituting phosphomimetic aspartate for serine/threonine residues in the Gln3 URS abolishes the N-terminal Gln3-Tor1 interaction, rapamycin-elicited nuclear Gln3 localization, and ½ of the derepressed levels of nuclear Gln3 localization. Cytoplasmic Gln3 sequestration in repressive conditions, however, remains intact. These findings further deconvolve the mechanisms that achieve nitrogen-responsive transcription factor regulation downstream of TorC1.

Sensing, Uptake and Catabolism of L-Phenylalanine During 2-Phenylethanol Biosynthesis via the Ehrlich Pathway in Saccharomyces cerevisiae

2-Phenylethanol (2-PE) is an important flavouring ingredient with a persistent rose-like odour, and it has been widely utilized in food, perfume, beverages, and medicine. Due to the potential existence of toxic byproducts in 2-PE resulting from chemical synthesis, the demand for “natural” 2-PE through biotransformation is increasing. L-Phenylalanine (L-Phe) is used as the precursor for the biosynthesis of 2-PE through the Ehrlich pathway by Saccharomyces cerevisiae. The regulation of L-Phe metabolism in S. cerevisiae is complicated and elaborate. We reviewed current progress on the signal transduction pathways of L-Phe sensing, uptake of extracellular L-Phe and 2-PE synthesis from L-Phe through the Ehrlich pathway. Moreover, the anticipated bottlenecks and future research directions for S. cerevisiae biosynthesis of 2-PE are discussed.

Sit4 and PP2A Dephosphorylate Nitrogen Catabolite Repression-Sensitive Gln3 When TorC1 Is Up- as Well as Downregulated

Saccharomyces cerevisiae lives in boom and bust nutritional environments. Sophisticated regulatory systems have evolved to rapidly cope with these changes while preserving intracellular homeostasis. Target of Rapamycin Complex 1 (TorC1), is a serine/threonine kinase complex and a principle nitrogen-responsive regulator. TorC1 is activated by excess nitrogen and downregulated by limiting nitrogen. Two of TorC1's many downstream targets are Gln3 and Gat1-GATA-family transcription activators-whose localization and function are Nitrogen Catabolite Repression- (NCR-) sensitive. In nitrogen replete environments, TorC1 is activated, thereby inhibiting the PTap42-Sit4 and PTap42-PP2A (Pph21/Pph22-Tpd3, Pph21,22-Rts1/Cdc55) phosphatase complexes. Gln3 is phosphorylated, sequestered in the cytoplasm and NCR-sensitive transcription repressed. In nitrogen-limiting conditions, TorC1 is downregulated and PTap42-Sit4 and PTap42-PP2A are active. They dephosphorylate Gln3, which dissociates from Ure2, relocates to the nucleus, and activates transcription. A paradoxical observation, however, led us to suspect that Gln3 control was more complex than appreciated, i.e., Sit4 dephosphorylates Gln3 more in excess than in limiting nitrogen conditions. This paradox motivated us to reinvestigate the roles of these phosphatases in Gln3 regulation. We discovered that: (i) Sit4 and PP2A actively function both in conditions where TorC1 is activated as well as down-regulated; (ii) nuclear Gln3 is more highly phosphorylated than when it is sequestered in the cytoplasm; (iii) in nitrogen-replete conditions, Gln3 relocates from the nucleus to the cytoplasm, where it is dephosphorylated by Sit4 and PP2A; and (iv) in nitrogen excess and limiting conditions, Sit4, PP2A, and Ure2 are all required to maintain cytoplasmic Gln3 in its dephosphorylated form.

Glycolytic flux in Saccharomyces cerevisiae is dependent on RNA polymerase III and its negative regulator Maf1

Protein biosynthesis is energetically costly, is tightly regulated and is coupled to stress conditions including glucose deprivation. RNA polymerase III (RNAP III)-driven transcription of tDNA genes for production of tRNAs is a key element in efficient protein biosynthesis. Here we present an analysis of the effects of altered RNAP III activity on the Saccharomyces cerevisiae proteome and metabolism under glucose-rich conditions. We show for the first time that RNAP III is tightly coupled to the glycolytic system at the molecular systems level. Decreased RNAP III activity or the absence of the RNAP III negative regulator, Maf1 elicit broad changes in the abundance profiles of enzymes engaged in fundamental metabolism in S. cerevisiae In a mutant compromised in RNAP III activity, there is a repartitioning towards amino acids synthesis de novo at the expense of glycolytic throughput. Conversely, cells lacking Maf1 protein have greater potential for glycolytic flux.

The flavonoid 4,4'-dimethoxychalcone promotes autophagy-dependent longevity across species

Ageing constitutes the most important risk factor for all major chronic ailments, including malignant, cardiovascular and neurodegenerative diseases. However, behavioural and pharmacological interventions with feasible potential to promote health upon ageing remain rare. Here we report the identification of the flavonoid 4,4'-dimethoxychalcone (DMC) as a natural compound with anti-ageing properties. External DMC administration extends the lifespan of yeast, worms and flies, decelerates senescence of human cell cultures, and protects mice from prolonged myocardial ischaemia. Concomitantly, DMC induces autophagy, which is essential for its cytoprotective effects from yeast to mice. This pro-autophagic response induces a conserved systemic change in metabolism, operates independently of TORC1 signalling and depends on specific GATA transcription factors. Notably, we identify DMC in the plant Angelica keiskei koidzumi, to which longevity- and health-promoting effects are ascribed in Asian traditional medicine. In summary, we have identified and mechanistically characterised the conserved longevity-promoting effects of a natural anti-ageing drug.