Project description:In this study, we characterize the protein uptake and degradation pathways of S. cerevisiae to better understand its impact on protein secretion titers. We do find that S. cerevisiae can consume significant (g/L) quantities of whole proteins. Characterizing the systems with metabolomics and transcriptomics, we identify metabolic and regulatory markers that are consistent with uptake of whole proteins by endocytosis, followed by intracellular degradation and catabolism of substituent amino acids. Uptake and degradation of recombinant protein products may be common in S. cerevisiae protein secretion systems, and the current data should help formulate strategies to mitigate product loss.
Project description:When eukaryotic cells are deprived of amino acids, uncharged tRNAs accumulate and activate the conserved GCN2 protein kinase. We examine how yeast growth and tRNA charging or aminoacylation is affected during amino acid depletion in the presence and absence of GCN2. tRNA charging is measured using a microarray technique which allows for simultaneous measurement of all cytosolic tRNAs. A fully prototrophic and its isogenic GCN2 deletion strain were used.
Project description:Purpose: The exosome plays major roles in RNA processing and surveillance but the in vivo target range and substrate acquisition mechanisms remain unclear. We applied an in vivo cross-linking technique coupled with deep sequencing (CRAC) that captures transcriptome-wide interactions between individual yeast exosome subunits and their targets in a living cell. Methods: We apply CRAC to HTP-tagged proteins (HTP: His6 - TEV cleavage site - two copies of the z-domain of Protein A): Two nucleases (Rrp44, Rrp6) and two structural subunits (Rrp41, Csl4) of the yeast exosome. At least two independent experiments were performed in each case and analyzed separately. We performed CRAC on wild-type (WT) Rrp44 and two catalytic mutants, rrp44-endo (D91N, E120Q, D171N, D198N) and rrp44-exo (D551N). We further developed CRAC using cleavable proteins (split-CRAC) to compare endonuclease and exonuclease targets of Rrp44. Plasmids designed for split-CRAC contain a PreScission protease cleavage site (PP) inserted between aa 241 and 242 in the RRP44 ORF to allow in vitro cleavage of purified protein, and a His6 tag to select the respective cleaved fragment. Results: Analysis of wild-type Rrp44 and catalytic mutants showed that both the CUT and SUT classes of noncoding RNA, snoRNAs and, most prominently, pre-tRNAs and other Pol III transcripts are targeted for oligoadenylation and exosome degradation. Unspliced pre-mRNAs were also identified as targets for Rrp44 and Rrp6. CRAC performed using cleavable proteins (split-CRAC) revealed that Rrp44 endonuclease and exonuclease activities cooperate on most substrates. Mapping oligoadenylated reads suggests that the endonuclease activity may release stalled exosome substrates. Rrp6 was preferentially associated with structured targets, which frequently did not associate with the core exosome. This indicates that substrates can follow multiple pathways to the nucleases. Conclusion: Our study represents the first transcriptome-wide map of substrates for the yeast exosome nuclease complex. Identification of targets for individual exosome subunits in wild-type and mutant yeast cells.
Project description:When eukaryotic cells are deprived of amino acids, uncharged tRNAs accumulate and activate the conserved GCN2 protein kinase. We examine how yeast growth and tRNA charging or aminoacylation is affected during amino acid depletion in the presence and absence of GCN2. tRNA charging is measured using a microarray technique which allows for simultaneous measurement of all cytosolic tRNAs. A fully prototrophic and its isogenic GCN2 deletion strain were used. We measured relative tRNA charging levels in yeast strains with an intact and deleted GCN2.
Project description:Aminoacyl-tRNA synthetases (aaRSs) are essential enzymes that ligate amino acids to tRNAs, and often require editing to ensure accurate protein synthesis. Recessive mutations in aaRSs cause various neurological disorders in humans, yet the underlying mechanism remains poorly understood. Pathogenic aaRS mutations frequently cause protein destabilization and aminoacylation deficiency. In this study, we report that combined aminoacylation and editing defects cause severe proteotoxicity. We show that a C268A mutation in yeast threonyl-tRNA synthetase (ThrRS) abolishes editing and causes heat sensitivity. Surprisingly, directed-evolution of the C268A mutant result in intragenic mutations that restore heat resistance but not editing. C268A destabilizes ThrRS and decreases overall Thr-tRNAThr synthesis, and the suppressor mutations in the evolved strains improve aminoacylation. We further show that deficiency in ThrRS aminoacylation or editing alone is not sufficient to cause heat sensitivity, and that C268A impairs ribosome-associated quality control. Our results suggest that aminoacylation deficiency predisposes cells to proteotoxic stress.
Project description:In this study, we characterize the protein uptake and degradation pathways of S. cerevisiae to better understand its impact on protein secretion titers. We do find that S. cerevisiae can consume significant (g/L) quantities of whole proteins. Characterizing the systems with metabolomics and transcriptomics, we identify metabolic and regulatory markers that are consistent with uptake of whole proteins by endocytosis, followed by intracellular degradation and catabolism of substituent amino acids. Uptake and degradation of recombinant protein products may be common in S. cerevisiae protein secretion systems, and the current data should help formulate strategies to mitigate product loss. Saccharomyces cerevisiae strains at different cultivation conditions were selected at early glucose phase in batch fermentations for RNA extraction and hybridization on Affymetrix microarrays. Biological triplicates were applied, and strains growing at normal conditions (with no BSA supplemented) were used as the control strain.
Project description:Purpose: The exosome plays major roles in RNA processing and surveillance but the in vivo target range and substrate acquisition mechanisms remain unclear. We applied an in vivo cross-linking technique coupled with deep sequencing (CRAC) that captures transcriptome-wide interactions between individual yeast exosome subunits and their targets in a living cell. Methods: We apply CRAC to HTP-tagged proteins (HTP: His6 - TEV cleavage site - two copies of the z-domain of Protein A): Two nucleases (Rrp44, Rrp6) and two structural subunits (Rrp41, Csl4) of the yeast exosome. At least two independent experiments were performed in each case and analyzed separately. We performed CRAC on wild-type (WT) Rrp44 and two catalytic mutants, rrp44-endo (D91N, E120Q, D171N, D198N) and rrp44-exo (D551N). We further developed CRAC using cleavable proteins (split-CRAC) to compare endonuclease and exonuclease targets of Rrp44. Plasmids designed for split-CRAC contain a PreScission protease cleavage site (PP) inserted between aa 241 and 242 in the RRP44 ORF to allow in vitro cleavage of purified protein, and a His6 tag to select the respective cleaved fragment. Results: Analysis of wild-type Rrp44 and catalytic mutants showed that both the CUT and SUT classes of noncoding RNA, snoRNAs and, most prominently, pre-tRNAs and other Pol III transcripts are targeted for oligoadenylation and exosome degradation. Unspliced pre-mRNAs were also identified as targets for Rrp44 and Rrp6. CRAC performed using cleavable proteins (split-CRAC) revealed that Rrp44 endonuclease and exonuclease activities cooperate on most substrates. Mapping oligoadenylated reads suggests that the endonuclease activity may release stalled exosome substrates. Rrp6 was preferentially associated with structured targets, which frequently did not associate with the core exosome. This indicates that substrates can follow multiple pathways to the nucleases. Conclusion: Our study represents the first transcriptome-wide map of substrates for the yeast exosome nuclease complex.