Decoding the secrets of life with single-molecular translatomics: A revolutionary strategy in biology

The central dogma of molecular biology outlines the flow of sequence information from nucleic acids to proteins; however, transcript abundance serves as an imperfect surrogate for proteome composition. Indeed, mRNA levels account for only ∼40% of the variance in protein abundance, with translation rate, rather than transcription, dictating cellular protein output.1 In contrast, translatomics, which entails the genome-wide quantification of actively translating mRNAs, provides a functional readout of gene expression that surpasses the resolution of transcriptomics. While established techniques, including polysome profiling, ribosome profiling (Ribo-seq), and translating ribosome affinity purification (TRAP), have significantly propelled the study of translational control, their coupling with conventional sequencing has relied primarily on short-read cDNA libraries. Consequently, the native, full-length mRNA molecules engaged by ribosomes remain largely unexplored. Recent breakthroughs in DRS2 now enable the direct examination of native RNA molecules. If ONT DRS is coupled with mRNAs isolated from translation-associated fractions, it will profile the traits of translating mRNAs. In this review, we assess existing translatome methodologies and envisage the promising prospect of single-molecule translatomics.

Methods for translatome profiling

Polysome profiling was originally conceptualized based on RNA-linked multi-ribosome complexes engaged in protein synthesis. Subsequent sucrose-gradient-based polysome analysis facilitated the separation of mRNAs according to their degree of ribosome association. When integrated with RNA sequencing (RNA-seq), polysome-seq serves as a genome-wide proxy for transcript-level ribosome occupancy; however, its capacity to resolve transcript isoforms, untranslated region (UTR) architecture, and poly(A)-tail characteristics is constrained by the limitations of short-read libraries.

For instance, Ribo-seq yields only ribosome footprints, precluding identification of the specific transcript isoform being translated, as well as the resolution of phased modifications and poly(A) tails on individual molecules. TRAP-seq and RiboTag enable the retrieval of epitope-tagged ribosomes from specific cell types in vivo, while ribosome–nascent chain complex-bound mRNA sequencing (RNC-seq) isolates intact ribosome-nascent-chain complexes to recover full-length translating mRNAs. Transcript isoforms in polysomes sequencing (TrIP-seq) pioneered isoform-aware polysome profiling, demonstrating that alternative 5′ and 3′ UTR isoforms can drive up to 100-fold differences in translational output,3 yet it remained reliant on short Illumina reads.

Collectively, these methodologies are hampered by three fundamental structural limitations: reverse transcription and PCR introduce sequence and length biases; chemical modifications and poly(A) tails are lost during library preparation; and short reads fail to associate distal exons, UTRs, modifications, and poly(A) tails with a single translating molecule.