Project description:We measured the effect of codons on mRNA stability in zebrafish embryos using reporter mRNAs. We showed that slow decoding of codons by the ribosome promoted mRNA degradation in zebrafish.
Project description:We measured the effect of codons on mRNA stability in zebrafish embryos using reporter mRNAs. We showed that slow decoding of codons by the ribosome promoted mRNA degradation in zebrafish.
Project description:We measured the effect of codons on mRNA stability in zebrafish embryos using reporter mRNAs. We showed that slow decoding of codons by the ribosome promoted mRNA degradation in zebrafish.
Project description:Messenger RNA (mRNA) stability substantially impacts steady-state gene expression levels in a cell. mRNA stability is strongly affected by codon composition in a translation-dependent manner across species, through a mechanism termed codon optimality. We have developed iCodon (www.iCodon.org), an algorithm for customizing mRNA expression through the introduction of synonymous codon substitutions into the coding sequence. iCodon is optimized for four vertebrate transcriptomes: mouse, human, frog, and fish. Users can predict the mRNA stability of any coding sequence based on its codon composition and subsequently generate more stable (optimized) or unstable (deoptimized) variants encoding for the same protein. Further, we show that codon optimality predictions correlate with both mRNA stability using a massive reporter library and expression levels using fluorescent reporters and analysis of endogenous gene expression in zebrafish embryos and/or human cells. Therefore, iCodon will benefit basic biological research, as well as a wide range of applications for biotechnology and biomedicine.
Project description:Protein translation depends on mRNA-specific initiation, elongation, and termination rates. While the regulation of ribosome elongation is well studied in bacteria and yeast, less is known in higher eukaryotes. Here, we combined ribosome and tRNA profiling to investigate the relations between ribosome elongation rates, (aminoacyl-) tRNA levels and codon usage in mammals. We modeled codon-specific ribosome dwell times and translation fluxes from ribosome profiling, considering pair-interactions between ribosome sites. In mouse liver, the model revealed site and codon specific dwell times, as well as codon pair-interactions clustering by amino acids. While translation fluxes varied significantly across diurnal time and feeding regimen, codon dwell times were highly stable, and conserved in human. Fasting had no effect on codon dwell times in mouse liver. Profiling of total and aminoacylated tRNAs revealed highly heterogeneous levels with specific isoacceptor patterns and a correlation with codon usage. tRNAs for isoleucine, asparagine, aspartate and arginine were lowly loaded and conserved in fasted mice. Finally, codons with low levels of charged tRNAs and high codon usage relative to tRNA abundance exhibited long dwell times. Together, these analyses pave the way towards understanding the complex relation between tRNA loading, codon usage and ribosome dwell times in mammals.
Project description:A ELMSeq reporter cassette was created to monitor Dam levels by methylation, and introduced in the genome. The regions of 6 nt upstream and 6 nt downstream the stop codon were randomized to study their effect on gene expression. The ELMSeq reporter cassette was composed of: promoter - dam - random N6 - stop codon TAA - random N6 - spacer - 4xGATC. The amplicon was spanning the C-terminal region. The cassette was introduced in Mycoplasma pneumoniae.
Project description:The ribosome-associated quality control (RQC) is a surveillance system for aberrant translation, sensing ribosome collisions. Although the molecular mechanism has been extensively studied, the endogenous targets of RQC in human cells were poorly understood. Here, starting from the study of codon specificity of eukaryotic termination factor eRF1, we unexpectedly find that misrecognition of UUA sense codon by eRF1 leads to ribosome collisions and provides the source of RQC substrates in humans. eRF1-selective Monosome-Seq and Disome-Seq reveal that eRF1 recruitment to ribosome was not restricted to the stop codons but also the sub-cognate sense codons, including the UUA codon. The UUA misrecognition by eRF1 causes ribosome collision without termination reaction. Remarkably, Disome-Seq with the depletion of ASCC3 and 4EHP, key factors in RQC, showed that ribosome stalled at UUA codons are the predominant sub-populations rescued by RQC. Failure to resolve ribosome collisions by RQC triggers p38 phosphorylation and upregulation of stress response transcription factor ATF3. This study presents the impact of sense codon misrecognition by the termination factor on translation homeostasis in human cells.