Project description:Usage of synonymous codons represents a characteristic pattern of preference in each organism. It has been inferred that such bias of codon usage has evolved as a result of adaptation for efficient synthesis of proteins. Here we examined synonymous codon usage in genes of the fission yeast Schizosaccharomyces pombe, and compared codon usage bias with expression levels of the gene. In this organism, synonymous codon usage bias was correlated with expression levels of the gene; the bias was most obvious in two-codon amino acids. A similar pattern of the codon usage bias was also observed in Saccharomyces cerevisiae, Arabidopsis thaliana, and Caenorhabditis elegans, but was not obvious in Oryza sativa, Drosophila melanogaster, Takifugu rubripes and Homo sapiens. As codons of the highly expressed genes have greater influence on translational efficiency than codons of genes expressed at lower levels, it is likely that codon usage in the S. pombe genome has been optimized by translational selection through evolution. Relative amounts of mRNA for each ORF were measured by DNA microarray using genomic DNA as a reference, and the copy number of mRNA was calculated using an estimate of the total mRNA number in the cell as 100,000 copies.
Project description:Differences in codon frequency between genomes, genes, or positions along a gene, modulate transcription and translation efficiency, leading to phenotypic and functional differences. Integrative studies quantifying the phenotypic consequences of codon usage bias at different molecular and cellular levels in human cells are lacking. Here, we present a multiscale analysis of the effects of synonymous codon recoding during heterologous gene expression in human cells. Six synonymous versions of an antibiotic resistance gene were generated, fused to a fluorescent reporter, and independently expressed in HEK293 cells. Multiscale phenotype was analysed by means of: quantitative transcriptome and proteome assessment, as proxies for gene expression; cellular fluorescence, as a proxy for single-cell level expression; and real-time cell proliferation in absence or presence of antibiotic, as a proxy for the cell fitness. We show that differences in codon usage bias strongly impact the molecular and cellular phenotype: (i) they result in large differences in mRNA and in protein levels, as well in mRNA-to-protein ratio; (ii) they introduce unpredicted splicing events; (iii) they lead to reproducible phenotypic heterogeneity; and (iv) they lead to a trade-off between the benefit of antibiotic resistance and the burden of heterologous expression. In human cells in culture, codon usage bias modulates gene expression by modifying mRNA availability and suitability for translation, leading to differences in protein levels and eventually eliciting functional phenotypic changes.
Project description:The protein content determines the cell state. The variation in protein abundance is crucial when organisms are in the early stages of heat stress, but the reasons affecting their changes are largely unknown. We quantified 47,535 mRNAs and 3,742 proteins in filling grain of wheat under two thermal environments. The impact of mRNA abundance and sequence features which implicated in protein translation and degradation on protein expression was evaluated by regression analysis. Transcription, codon usage and amino acid frequency mainly drive the changes in protein expression under heat stress, and their combined contribution explains 58.2% and 66.4% of protein variation in 30 and 40 °C, respectively. Of which, transcription contributes more to the alteration in protein content under 40 °C (31%) than to 30 °C (6%). Codon usage plays a stable and powerful role in protein expression under heat stress, even surpassing transcription. What’s more, the usage of AAG is a key factor regulating rapid protein expression under heat stress.
Project description:The uneven use of synonymous codons in the transcriptome regulates the efficiency and fidelity of protein translation rates. Yet, the importance of this codon bias on regulating cell state-specific expression programs is currently debated. Here, we asked whether the gene expression program in the well-defined cell states of self-renewal and differentiation in embryonic stem cells is driven by optimized codon usage. Using ribosome and transcriptome profiling, we identified distinct codon signatures for human self-renewing and differentiating embryonic stem cells. One driver for the cell state-specific codon bias was the genomic GC-content of the differentially expressed genes and thus, determined by transcription rather than translation. However, by measuring the codon frequencies at the ribosome’s active sites interacting with transfer RNAs (tRNA), we discovered that the wobble position tRNA modification inosine strongly influenced the codon optimization in self-renewing embryonic stem cells. This effect was conserved in mice and independent of the differentiation stimulus. In summary, we newly reveal how translational mechanisms based on RNA modifications can shape optimized codon usage in embryonic stem cells.
Project description:The uneven use of synonymous codons in the transcriptome regulates the efficiency and fidelity of protein translation rates. Yet, the importance of this codon bias on regulating cell state-specific expression programs is currently debated. Here, we asked whether the gene expression program in the well-defined cell states of self-renewal and differentiation in embryonic stem cells is driven by optimized codon usage. Using ribosome and transcriptome profiling, we identified distinct codon signatures for human self-renewing and differentiating embryonic stem cells. One driver for the cell state-specific codon bias was the genomic GC-content of the differentially expressed genes and thus, determined by transcription rather than translation. However, by measuring the codon frequencies at the ribosome’s active sites interacting with transfer RNAs (tRNA), we discovered that the wobble position tRNA modification inosine strongly influenced the codon optimization in self-renewing embryonic stem cells. This effect was conserved in mice and independent of the differentiation stimulus. In summary, we newly reveal how translational mechanisms based on RNA modifications can shape optimized codon usage in embryonic stem cells.