Project description:As compared to Eukaryotes, Bacteria have a reduced tRNA gene set encoding between 30 and 220 tRNAs, which are thought to act in concert for the maintenance of gene translation. Here we show that in some bacteria the tRNA gene set may be partitioned in a housekeeping sub-set that sustains translation, and an inducible one that is generally silent but can be largely induced to provide functionality under particular conditions. In the model cyanobacterium Anabaena sp. PCC 7120, the inducible set forms an operon encoding 23 functional tRNAs. Transcription of these tRNAs is induced by translation stress, i.e. by insults that impair translation, including antibiotics that target the ribosome. The operon is co-regulated with genes encoding proteins like the tRNA ligase RtcB and the stress-specific protein DpsA, probably involved in a response directed to protect the cell and recover translation. Common regulation suggests participation of operonic tRNAs in this response, although mechanistic issues remain to be determined. Similar long tRNA gene operons were found in species across major bacterial phyla and are shown to be distinct in many aspects from other operons that evolved by gene accretion.
Project description:In the ribosome complex, tRNA is a critical element of mRNA translation. We reported a new technology for profiling ribosome-embedded tRNAs and their modifications. With the method, we generated a comprehensive survey of the quanity and quality of intra-ribosomal tRNAs (Ribo-tRNA-seq). Ribo-tRNA-seq can provide new insights on translation control mechanism in diverse biological contexts.
Project description:The Synthetase Sequestration Model (SSM) is a simplified translation model that considers explicitly two main steps in the process of tRNA aminoacylation: first, the tRNA is bound by the aminoacyl tRNA synthetase, and in a second step, the amino acid is attached to the tRNA. The tRNA then participates in the translation reaction, becoming deacylated as a result. The tRNA exists in states bound, charged and uncharged. In the bound state, the tRNA is bound to the synthetase but uncharged, i.e., the tRNA is sequestered by the synthetase. The model predicts how the balance between the three different tRNA states (empty, bound and charged) changes depending on aminoacyl tRNA synthetase availability.
Project description:Analysis of the peptides and proteins synthesized in a cell-free translation system containing either the natural tRNA extract, the hybrid-SL tRNA set, or the hybrid-SL tRNA set minus one chimeric tRNA using LC-MS.
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.
Project description:The cancer cells selectively promote translation of specific oncogenic transcripts to facilitate cancer survival and progression, while the underlying mechanisms are poorly understood. N7-methylguanosine (m7G) tRNA modification and its methyltransferase complex METTL1/WDR4 are significantly up-regulated in intrahepatic cholangiocarcinoma (ICC) and associated with poor prognosis. We developed tRNA reduction and cleavage sequencing (TRAC-Seq) to reveal the m7G tRNA methylome inICC cell line and ribosome nascent-chain complex-bound mRNAs sequencing(RNC-seq) and ribosome profiling(Ribo-seq) to study the differential translated genes and reveal the ribosome pausing. A subset of 22 tRNAs is modified at a ‘RAGGU’ motif within the variable loop. We observe increased ribosome occupancy at the corresponding codons in the Mettl1 knockdown ICC cell line implying widespread effects on tRNA function, ribosome pausing, and mRNA translation. Translation of cell cycle genes and EGFR signaling pathway genes is particularly affected. Our study uncovers the important physiological function and mechanism of METTL1-mediated m7G tRNA modification in the regulation of cancer progression.
Project description:We investigated cryptic transcription start site usage, chromatin organization and post-transcriptional consequences in Saccharomyces cerevisiae. We used 5PSeq approach, which measures ribosome dynamics by sequencing the presence of co-translation mRNA degradation intermediates, to assess if cryptic transcripts are engaged in active translation. We show that chromatin-dependent cryptic transcripts can be recognized by ribosomes and have the potential to produce truncated polypeptides by using downs-stream, in-frame start codons. Our work suggests that a significant fraction of chromatin-dependent internal cryptic promoters are in fact alternative truncated mRNA isoforms.
Project description:Quantitative and qualitative changes in mRNA translation occur in tumor cells and support cancer progression and metastasis. Post-transcriptional nucleoside modifications of transfer RNAs (tRNAs) at the wobble U34 base are highly conserved and contribute to translation fidelity. Here, we show that ELP3 and CTU1/2, partner enzymes in U34 mcm5s2-tRNA modification, are upregulated in human breast cancers and sustain metastasis. Elp3 genetic ablation strongly impaired invasion and metastasis formation in the PyMT model of invasive breast cancer. Mechanistically, ELP3 and CTU1/2 support cellular invasion through the translation of the oncoprotein DEK. As a result, DEK promotes the IRES-dependent translation of the pro-invasive transcription factor LEF1. Consistently, a DEK mutant, whose codon composition is independent of U34 mcm5s2-tRNA modification, escapes the ELP3- and CTU1-dependent regulation and restores the IRES-dependent LEF1 expression. Our results demonstrate the key role of U34 tRNA modification to support specific translation during breast cancer progression and highlight a functional link between tRNA modification- and IRES-dependent translation during tumor cell invasion and metastasis.analysis of transcriptomic changes due to Elp3genetic deletion in cells extracted from PyMT mammary tumors.
Project description:The stability of mRNA is an important determinant of its abundance and, consequently, protein production. There has been extensive research on the pathways governing mRNA stability and translation, however, it is unclear the extent to which these processes are modulated by environmental conditions. We previously modelled rapid recovery gene down-regulation (RRGD) following light stress in Arabidopsis thaliana (Arabidopsis) using mathematical calculations to account for transcription in order to predict half-lives and led to the hypothesis of recovery-specific transcript destabilisation. Here, we test this hypothesis by quantifying changes in transcription, mRNA stability, and translation in leaves of mature Arabidopsis undergoing light stress and recovery and investigate processes regulating transcript abundance and fate. Compared to juvenile plants from prior work, here we find that stability is altered for a range of transcripts that encode proteins involved in post-transcriptional processes in mature leaves. We also observe transcript destabilisation during light stress, followed by re-stabilisation upon recovery. Alongside this, we observe fast transcriptional shut-off in recovery that, when paired with transcript destabilisation, promotes rapid down-regulation of stress-induced genes. Translation was dynamic over the course of light stress and recovery, with substantial transcript-specific increases in polysome loading observed during late stress independently of total mRNA abundance. Taken together, we provide evidence for the combinatorial regulation of transcription, mRNA stability, and translation that occurs during light stress and recovery.