mRNA Tail Sequences Act as Protein Chaperones to Prevent Misfolding
Scientists discover that 3' UTRs of mRNAs actively guide protein folding during translation, controlling activity of key cancer and aging regulators.
Summary
Researchers at Memorial Sloan Kettering have uncovered a surprising new function for the non-coding 'tails' of messenger RNA molecules. More than 2,700 human mRNAs carry highly conserved sequences in their 3' untranslated regions (UTRs) whose purpose was unknown. This study shows these sequences act as molecular chaperones, guiding the folding of proteins that contain long disordered regions — flexible protein segments involved in regulating genes, including cancer-driving proteins like MYC. Without the RNA chaperone, these proteins can misfold and lose function. This challenges a core assumption in molecular biology: that the protein sequence alone determines how a protein folds and what it does. The findings suggest a hidden layer of gene regulation embedded in RNA structure, with implications for understanding cancer, aging, and diseases caused by protein misfolding.
Detailed Summary
For decades, molecular biology has assumed that a protein's amino acid sequence fully determines its three-dimensional shape and function. A landmark study from the Mayr Lab at Memorial Sloan Kettering Institute now challenges that dogma, revealing that the 3' untranslated regions (3' UTRs) of mRNAs — sequences once dismissed as regulatory afterthoughts — actively chaperone protein folding during translation itself.
The researchers identified over 2,700 human mRNAs bearing hundreds of highly conserved nucleotides in their 3' UTRs. Notably, these mRNAs disproportionately encode proteins containing long intrinsically disordered regions (IDRs) — flexible, unstructured protein segments rich in hydrophobic amino acid clusters. IDR-containing proteins are critical regulators of transcription and are frequently dysregulated in cancer and aging.
Focusing on three proteins — MYC, UTX, and JMJD3 — the team demonstrated that 3' UTR sequences directly control protein activity. For JMJD3 (encoded by KDM6B), the 3' UTR co-translationally alters how the protein folds: promoting IDR-to-IDR interactions while preventing hydrophobic IDR clusters from interfering with proper folding of adjacent structured domains. Without the 3' UTR, proteins misfold and lose activity — not because they're absent, but because they're improperly assembled.
Mechanistically, 3' UTRs with chaperone activity are multivalent and localize to condensate-enriched environments, suggesting cells create specialized local microenvironments to correctly fold IDR-containing proteins at the moment of their synthesis. This places RNA itself — not just proteins — in the role of folding guardian.
The implications span cancer biology, transcriptional regulation, and potentially aging, where IDR-containing regulators of chromatin and gene expression are frequently impaired. The discovery of RNA-based co-translational chaperone activity opens an entirely new axis of gene regulation to explore and potentially target therapeutically.
Key Findings
- Over 2,700 human mRNA 3' UTRs carry conserved sequences that control activity of IDR-containing proteins.
- 3' UTRs act as co-translational chaperones, shaping protein folding without altering protein abundance or location.
- Without 3' UTR chaperone activity, transcriptional regulators like JMJD3 and MYC misfold and lose function.
- Protein sequence alone is insufficient for correct folding of IDR-containing proteins — the mRNA is required.
- Chaperone-active 3' UTRs localize to condensate-enriched environments, creating specialized folding microenvironments.
Methodology
The study used molecular and cellular experiments in human cells, examining three model IDR-containing proteins (MYC, UTX, JMJD3) with and without their cognate 3' UTRs. Folding states and domain interactions were assessed co-translationally. The study was conducted at a major cancer research institution using biochemical, structural, and cell biology approaches, though specific assay details are not available from the abstract alone.
Study Limitations
This summary is based on the abstract only, as the full paper is not open access; detailed methods, quantitative data, and supplementary findings are unavailable. The study demonstrates the phenomenon for three specific proteins and may not generalize uniformly across all 2,700 identified mRNAs. Causal mechanisms are proposed but the full structural and biochemical basis of RNA chaperone activity remains to be deeply characterized.
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