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RNA codon expansion via programmable pseudouridine editing and decoding

An Author Correction to this article was published on 11 August 2025

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Abstract

The incorporation of non-canonical amino acids (ncAAs) enables customized chemistry to tailor protein functions1,2,3. Genetic code expansion offers a general approach for ncAA encoding by reassigning stop codons as the ‘blank’ codon; however, it is not completely orthogonal to translation termination for cellular transcripts. Here, to generate more bona fide blank codons, we developed an RNA codon-expansion (RCE) strategy that introduces and decodes bioorthogonally assignable pseudouridine (Ψ) codons (ΨGA, ΨAA or ΨAG) on specified mRNA transcripts to incorporate ncAAs in mammalian cells. The RCE strategy comprises a programmable guide RNA4, an engineered decoder tRNA, and aminoacyl-tRNA synthetase. We first developed the RCE(ΨGA) system, which incorporates functional ncAAs into proteins via the ΨGA codon, demonstrating a higher translatome-wide and proteomic specificity compared with the genetic code expansion system. We further expanded our strategy to produce the RCE(ΨAA) and RCE(ΨAG) systems, with all three Ψ codon:(Ψ codon)-tRNAPyl pairs exhibiting mutual orthogonality. Moreover, we demonstrated that the RCE system cooperates compatibly with the genetic code expansion strategy for dual ncAA encoding. In sum, the RCE method utilized Ψ as a post-transcriptional ‘letter’ to encode and decode RNA codons in specific mRNA transcripts, opening a new route for genetic alphabet expansion and site-specific ncAA incorporation in eukaryotic cells.

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Fig. 1: Schematic overview of the RCE strategy and yields of encoded ΨGA codon in the specified mRNA transcript.
Fig. 2: Screening and evaluation of the specific and efficient decoder tRNA for the ΨGA codon over the UGA codon.
Fig. 3: The RCE(ΨGA) system exhibited high translatome-wide decoding specificity without transcriptome-wide disturbance.
Fig. 4: RCE(ΨGA) enables site-specific ncAA incorporation and precise modulation of protein activity in living cells.
Fig. 5: The RCE strategy is expandable to other modified RNA codons and is compatible with the GCE strategy.

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Data availability

All next-generation sequencing data generated for this study have been deposited in the NCBI Sequence Read Archive (SRA) under accession code PRJNA1090628. The human reference genome GRCh38 (December 2013) was downloaded from the following link: https://hgdownload.soe.ucsc.edu. The H. sapiens proteome database (UP000005640) was downloaded from https://www.uniprot.org. The custom database containing reporter sequences featuring 20 different natural amino acids at positions corresponding to the premature termination codon location is provided in Supplementary Table 1. The tRNA reference sequences were derived from GtRNAdb81 (http://gtrnadb.ucsc.edu/; accessed September 2024). ISR-related genes were collected from the GeneCards database (https://www.genecards.org/; accessed September 2024). Source data are provided with this paper.

Code availability

Custom codes are available on GitHub (https://github.com/yanxueqing621/RCE_project). These scripts include the pipelines for off-target Ψ sites identification based on PRAISE sequencing data, evaluation of potential off-target readthrough events based on Ribo-seq data, and RNA-seq data analysis.

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Acknowledgements

The authors thank the National Center for Protein Sciences at Peking University in Beijing, China, for assistance with the 4150 TapeStation System (G. Li), mass spectrometry (D. Liu and Q. Zhang), Zeiss LSM 980 confocal microscope and Spin SR confocal microscope (L. Fu); G. Jia, R. Liu, F. Lin, X. Rao, C. Shao, M. Zhang and Y. Ma for discussions and materials; the Center for Quantitative Biology at Peking University for assistance with the ImageXpress Micro 4 high-content imaging system; and X. Li for help. Part of the analysis was performed on the High-Performance Computing Platform of the Center for Life Science (Peking University). We acknowledge funding from the National Natural Science Foundation of China (22137001 to P.R.C., 22337001 to C.Y., 92353000 to P.R.C. and 22425071 to C.Y.), the Ministry of Science and Technology (2023YFA1506500 and 2021YFA1302600 to P.R.C.; 2023YFC3402200 to C.Y.), Beijing Municipal Science and Technology Commission Project (Z231100002723005 to C.Y.), New Cornerstone Science Foundation (to C.Y.) through the XPLORER PRIZE, as well as New Cornerstone Science Foundation (to P.R.C.) through the New Cornerstone Investigator Program. This work was also supported by the Ministry of Agriculture and Rural Affairs of China.

Author information

Authors and Affiliations

Contributions

P.R.C., C.Y. and J.L. conceived the research. J.L. guided, designed and performed the experiments. X.Y. analysed the sequencing data. H. Wu analysed and organized the fluorescence data. Z.J. and Y.S. contributed in the screening, immunoprecipitation and proteomic experiments. X.W., R.G. and H. Wen conducted molecular dynamics simulation. Y.R. assisted the experiments in screening. C.L. performed acid-denaturing northern blots. Y.Z. and Z.J. guided the phosphoproteomic profiling. Y. M. conducted the tRNA sequencing and PRAISE sequencing experiments. All authors commented and approved the paper.

Corresponding authors

Correspondence to Chengqi Yi or Peng R. Chen.

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Competing interests

C.Y. is an inventor on patents related to the RESTART technology (PCT/CN2022/095172). The other authors declare no competing interests.

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Extended data figures and tables

Extended Data Fig. 1 The yields of ΨGA codons within targeted mRNAs under different dosage of gsnoRNA and PylRS-tRNAPyl.

a-c, The IGV views and ΨGA codon yields within three targeted reporters: LDLR-TGA (a), AGXT-TGA (b), and Screen-TGA (c) at 0%, 25%, 50%, and 100% of the corresponding guide snoRNA. d, The IGV views and ΨGA codon yields within targeted Screen-TGA reporter under zero, 1:1, 1:4 or 1:8 stoichiometry to PylRS-tRNAPyl. Data of bar plots are presented as the mean values (n = 2 biologically independent replicates).

Source Data

Extended Data Fig. 2 High encoding specificity of RCE strategy verified by the limited off-target Ψ edits as well as low off-target Ψ editing ratios across the transcriptome.

a, Complementary regions between gsnoRNA (black) and target site in SrcK295TGA-GFP reporter (blue). b, Complementary regions between gsnoRNA (black) and an off-target site in the endogenous gene (red). c, Sequence motif of the RCE-induced off-target Ψ sites. d, The on-target and off-target regions within the secondary structure of the gsnoRNA-Src predicted by RNAfold. The base-pair probabilities are indicated with color. Red and blue colors represent high and low probabilities, respectively. e,f IGV views representing the reads mapped at the off-target sites in 3’ UTRs of NM_001032283.3(e) and XM_017027173.2(f). g, Pie chart showing the distribution of RCE-induced off-target Ψ sites in the transcriptome. h, Scatterplot showing the expression level of genes containing the off-target Ψ sites by RNA-seq. Data are represented as the mean values (n = 2 biologically independent replicates). i, Scatterplot showing the translation level of genes containing the off-target Ψ sites by Ribo-seq. Data are represented as the mean values (n = 2 biologically independent replicates). The correlations between different conditions were measured via Pearson’s correlation score by defaulted parameters.

Source Data

Extended Data Fig. 3 Evaluating the ncAA incorporation fidelity of the RCE system.

a, Schematic illustration of the workflow for identifying peptides with different amino acid incorporation via LC-tandem MS. b-g, The RCE system allowed site-specific incorporation of ncAAs with high fidelity on the Venus-TGA (b), Screen-TGA (d), and Src-K295*-Y527F-GFP (f) reporters. The corresponding Venus-R (c), Screen-R (e), and Src-K295R-Y527F-GFP (g) reporters were used for comparison of natural amino acid incorporation. h-j, Acid denaturing Northern Blots illustrating that the decoder tRNAs were highly charged with ncAA in all three RCE systems: RCE (ΨGA) (h), RCE (ΨAG) (i), RCE (ΨAA) (j). Each experiment was independently repeated twice with similar results. k, Diagram of the integrated stress response pathway. l, Western blotting demonstrating that the integrated stress response was not activated in the RCE systems. Tunicamycin treatment is used as a control of ISR activation. Each experiment was independently repeated twice with similar results. m, Scatterplot showing the translation level of ISR-related genes measured by Ribo-seq. Data are represented as the mean values (n = 2 biologically independent replicates).

Source Data

Extended Data Fig. 4 MD simulation-based prediction supports the ΨGA preference of the screened mmtRNAPyl(UCA)-A37G variant.

a-c, Structural comparison among the ribosome-tRNA-mRNA complex from cryo-EM (PDB ID: 4JYA) (a), and all-atom MD simulation (b), along with the merged complex structures between cryo-EM and MD (c). The results show that the tRNA and mRNA align well between the structures from cryo-EM and MD simulation. d, The paired probability of the averaged trajectories demonstrating the binding between tRNA variants and UGA- or ΨGA-containing mRNAs. e-h, Centroids of the tRNA-mRNA paring structures of the wild-type mmtRNAPyl(UCA) (e,f) and the selected mmtRNAPyl(UCA)-A37G (g,h), illustrating that mmtRNAPyl(UCA)-37G forms more stable hydrogen bonds to ΨGA codon than to UGA codon.

Source Data

Extended Data Fig. 5 The RCE system exhibited a high translational specificity when the reporter construct was expressed at an endogenous level.

a, Incorporated tetrazine-containing ncAA—TetBu could be labeled with TCO-biotin via bioorthogonal ligation. b, Western blotting of N-terminal HA-tagged products demonstrating that the protein product of the on-target reporter was expressed at endogenous concentration. RS/(ΨGA)-tRNATet alone was used to show the readthrough of tRNATet on the UGA codon of targeted reporter. The experiment was independently repeated twice with similar results. c,d, Western blotting (c) and quantitative analysis (d) showing the biotin signal for the GCE and RCE systems, demonstrating that the RCE system exhibited a low mis-incorporation level close to the background levels of endogenous biotinylated proteins. Data of bar plots are presented as the mean values (n = 2 biologically independent experiments). e,f, Western blotting (e) and quantitative analysis (f) comparing the off-target TetBu incorporation of the GCE(UGA), RS/(ΨGA)-tRNATet alone, and RCE(ΨGA) systems, without the targeted reporter, further demonstrating the ncAA incorporation specificity of the RCE system. Data of bar plots are presented as the mean values (n = 2 biologically independent experiments).

Source Data

Extended Data Fig. 6 Proteome analysis demonstrated high translational specificity of the RCE(ΨGA) system.

a, Schematic illustration of the affinity-based enrichment method for detecting the biotinylated peptides. b,c, Volcano plots showing the ncAA-incorporated endogenous proteins induced by the RCE(ΨGA) system (b) and the GCE(UGA) system (c). Red dots represent ncAA-incorporated endogenous proteins. P-values were calculated by linear models and subsequently adjusted via the Benjamini-Hochberg method. X-axis is fold change of protein abundance in the GCE(UGA)- or RCE(ΨGA)-treated cells compared to the control cells.

Source Data

Supplementary information

Supplementary Information (download PDF )

Supplementary Methods, Supplementary Discussion, legends for Supplementary Tables 1–7, Supplementary Figs. 1–24 and references.

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Liu, J., Yan, X., Wu, H. et al. RNA codon expansion via programmable pseudouridine editing and decoding. Nature 643, 1410–1420 (2025). https://doi.org/10.1038/s41586-025-09165-x

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