Sulfur Amino Acids Regulate Translational Capacity and Metabolic Homeostasis through Modulation of tRNA Thiolation

Abstract

SUMMARY Protein translation is an energetically demanding process that must be regulated in response to changes in nutrient availability. Herein, we report that the thiolation status of wobble-uridine (U34) nucleotides present on lysine, glutamine or glutamate tRNAs reflects intracellular methionine and cysteine availability, and regulates cellular translational capacity and metabolic homeostasis. tRNA thiolation is important for growth under nutritionally challenging environments and required for efficient translation of genes enriched in lysine, glutamine, and glutamate codons, which frequently encode proteins important for translation and growth-specific processes. tRNA thiolation is down-regulated during sulfur starvation in order to decrease sulfur consumption and growth, and its absence leads to a compensatory increase in enzymes involved in methionine, cysteine, and lysine biosynthesis. Thus, tRNA thiolation enables cells to modulate translational capacity according to the availability of sulfur amino acids, establishing a functional significance for this conserved tRNA nucleotide modification in cell growth control.

An evolutionary approach uncovers a diverse response of tRNA 2-thiolation to elevated temperatures in yeast

“…Certain nucleoside methylations were reported to increase upon chemical stress, which might indicate a need for tighter structural rigidity (Chan et al 2010(Chan et al , 2012. Moreover, it has been proposed that tRNA modification changes might affect translation in response to stress (Begley et al 2007;Chan et al 2010Chan et al , 2012Bauer et al 2012;Laxman et al 2013). An interesting example is uridine at position 34 (U 34 ), which pairs with the wobble base of the codon.…”

A [3Fe-4S] cluster is required for tRNA thiolation in archaea and eukaryotes

“…This reaction causes conformational changes and prevents aminoacylation of tRNAs, resulting in accumulations of uncharged tRNAs that trigger stringent responses (1) U acts as an identity element in aminoacylation reactions (5-7), promotes tRNA binding to the ribosomal A-site (7), and prevents frameshifting during translation (8). Yeast mutants lacking the 2-thio modification have pleotropic phenotypes, such as defects in invasive growth (9), hypersensitivity to high temperature, rapamycin, caffeine, or oxidative stress (10,11), inability to maintain normal metabolic cycles (12), and protein misfolding and aggregation (13). In humans, impaired 2-thio modification of the mitochondrial tRNAs has been associated with acute infantile liver failure (14,15) and myoclonic epilepsy with ragged-red fibers (16,17 U34 biosynthesis are complicated, and some of the details (especially in archaea and eukaryotes) remain unclear because: (i) they usually involve a cascade of sulfur carrier proteins rather than a direct transfer from the ultimate sulfur donor to the substrate, (ii) some sulfur carrier proteins have multiple roles that deliver sulfur to a variety of cofactors and nucleosides, and (iii) the sulfur carriers vary significantly between different organisms.…”

Single yeast cells vary in transcription activity not in delay time after a metabolic shift

“…The origin of the delay upon methionine removal may therefore also be related to a general growth rate and stress-related signalling mechanism. The molecular details of this global response are currently subject to active research 54,55 .…”

“…In addition to methionine storage capacity, the regulatory roles of methionine and SAM can also contribute to the observed transcription response delay. Reduction of the intracellular methionine level is perceived by yeast and initiates several stress response mechanisms, such as a growth stop and, eventually, autophagy 54,55 . However, methionine has a particularly complicated role in cell survival and growth control 56 .…”