Project description:Post-transcriptional modifications are important for transfer RNAs (tRNAs) to be efficient and accurate in translation on the ribosome. The m1G37 modification on a subset of tRNAs in bacteria are generated by a conserved methyltransferase TrmD and is essential for bacterial growth. Previous studies showed that m1G37 has an important role in preventing translational frameshifting and also that this modification is coupled with aminoacylation of tRNAs for proline. Here we performed suppressor screening to isolate a mutant E. coli cell that lacks TrmD but is viable, and the whole-genome sequencing revealed several mutations on prolyl-tRNA synthetase (ProRS) gene conferring cell viability in the absence of TrmD. Biochemical assays confirmed uncoupling of m1G37 modification and aminoacylation, and cell-based assays uncovered the critical role of m1G37 in supporting Wobble decoding.
Project description:Transfer RNA (tRNA) modifications enhance the efficiency, specificity and fidelity of translation in all organisms. The anticodon modification mcm5s2U34 is required for normal growth and stress resistance in yeast; mutants lacking this modification have numerous phenotypes. Mutations in the homologous human genes are linked to neurological disease. The yeast phenotypes can be ameliorated by overexpression of specific tRNAs, suggesting that the modifications are necessary for efficient translation of specific codons. We determined the in vivo ribosome distributions at single codon resolution in yeast strains lacking mcm5s2U. We found accumulations at AAA, CAA, and GAA codons, suggesting that translation is slow when these codons are in the ribosomal A site, but these changes appeared too small to affect protein output. Instead, we observed activation of the GCN4-mediated stress response by a non- canonical pathway. Thus, loss of mcm5s2U causes global effects on gene expression due to perturbation of cellular signaling. WT yeast and mutants lacking anticodon tRNA modifications were grown in YPD, and subjected to ribosome footprint profiling (ribo-seq) and RNA-seq of poly-A selected RNA. Dataset contains biological replicates for WT, Δncs6 and Δuba4. Technical replicates were also performed for all RNA-seq datasets (using a different poly-A selection method).
Project description:Plants have evolved sophisticated mechanisms to regulate gene expression to activate immune responses against pathogen infections. However, how the translation system contributes to plant immunity is largely unknown. The evolutionarily conserved thiolation modification of tRNA ensures efficient decoding during translation. Here we show that tRNA thiolation is required for plant immunity in Arabidopsis. The Arabidopsis cgb mutant is hyper-susceptible to the pathogen Pseudomonas syringae. CGB encodes ROL5, a homolog of yeast NCS6 required for tRNA thiolation. ROL5 physically interacts with CTU2, a homolog of yeast NCS2. Mutations in either ROL5 or CTU2 result in loss of tRNA thiolation. Further analyses reveal that tRNA thiolation is required for both transcriptional reprogramming and translational reprogramming during immune responses. The translation efficiency of immune-related proteins reduces when tRNA thiolation is absent. Our study not only uncovers a new biological function of tRNA thiolation but also reveals a new mechanism for plant immunity.
Project description:Plants have evolved sophisticated mechanisms to regulate gene expression to activate immune responses against pathogen infections. However, how the translation system contributes to plant immunity is largely unknown. The evolutionarily conserved thiolation modification of tRNA ensures efficient decoding during translation. Here we show that tRNA thiolation is required for plant immunity in Arabidopsis. The Arabidopsis cgb mutant is hyper-susceptible to the pathogen Pseudomonas syringae. CGB encodes ROL5, a homolog of yeast NCS6 required for tRNA thiolation. ROL5 physically interacts with CTU2, a homolog of yeast NCS2. Mutations in either ROL5 or CTU2 result in loss of tRNA thiolation. Further analyses reveal that tRNA thiolation is required for both transcriptional reprogramming and translational reprogramming during immune responses. The translation efficiency of immune-related proteins reduces when tRNA thiolation is absent. Our study not only uncovers a new biological function of tRNA thiolation but also reveals a new mechanism for plant immunity.
Project description:N7-methylguanosine (m7G) in variable loop region of tRNA stabilizes target tRNA expression, which is catalyzed by METTL1/WDR4 heterodimer. Here, we unveil essential functions of Mettl1 in Drosophila fertility. Mettl1-knockout (Mettl1-KO) decreases elongated spermatid and mature sperm, which is fully rescued by Mettl1-transgene expression, but not catalytic dead Mettl1-transgene, demonstrating that Mettl1-dependent m7G is required for spermatogenesis. Mettl1-KO shows loss of m7G modification on subset of tRNAs and decreased level of tRNA expression. Strikingly, overexpression of translational elongation factor EF1α that can compete with rapid tRNA decay (RTD) pathway in S. cerevisiae, significantly counteract the sterility in Mettl1-KO male, supporting a critical role of m7G tRNA modification in spermatogenesis. Ribo-seq analysis shows that Mettl1-KO elevates ribosome collisions at codons decoded by reduced tRNAs and significantly reduces translation of genes involved in elongated spermatid formation and sperm stability. These findings reveal a developmental role for m7G tRNA modifications and suggest that m7G modification-dependent tRNA stability differs among tissues.
Project description:We report the identification and quantification of Watson-Crick modifications in tRNA and rRNA through the use of high throughput sequencing. We apply the recently published DM-tRNA-Seq method to generate demethylase treated and untreated 293T samples, and using computational methods we are able to flag sites using a modification index. This index allows us to generate site-resolved information about modification that we can use to identify and quantify Watson-Crick face modifications in tRNA and rRNA. With the demethylase treated samples, we are able to validate numerous nucleotide modifications from demethylase substrates, and the absence of demethylase action also serves to aid in identification. We find numerous novel modification sites in tRNA as well as striking comparisons between tissues cultures lines. Our study reports a comprehensive analysis of the tRNA modification landscape by identifying sites of modification as well as quantifying modification levels.
Project description:N7-methylguanosine (m7G) modification is one of the most prevalent tRNA modifications in human. The precise function and molecular mechanism of m7G tRNA modification in regulation of cancer remain poorly understood. Here we showed that m7G tRNA modification, METTL1 and WDR4 are elevated in hepatocellular carcinoma (HCC) tissues and associated with HCC patient prognosis. Functionally, silencing METTL1 or WDR4 inhibits HCC cell proliferation, migration and invasion, while forced expression of wild type METTL1 but not its catalytic dead mutant promotes HCC progression. Knockdown of METTL1 reduces m7G tRNA modification and decreases m7G modified tRNA expression. Mechanistically, METTL1 depletion selectively decreases the mRNA translation of a subset of oncogenic genes, especially cell cycle and EGFR pathway genes, in m7G-related codon dependent manner. Moreover, in vivo studies using Mettl1 knock-in and knockout mice reveal a critical function of Mettl1 mediated m7G tRNA modifications in promoting hepatocarcinogenesis in the hydrodynamics transfection HCC model. Our work uncovers the critical functions of tRNA m7G modification in regulating cancer mRNA translation and promoting hepatocarcinogenesis, thus provides new insights into role of the mis-regulated tRNA modifications in cancers.