Resurrection of a viral internal ribosome entry site from a 700 year old ancient Northwest Territories cripavirus
Bibliographic record
Abstract
ABSTRACT The dicistrovirus intergenic region internal ribosome entry site (IGR IRES) uses an unprecedented streamlined mechanism whereby the IRES adopts a triple-pseudoknot (PK) structure to directly bind to the conserved core of the ribosome and drive translation from a non-AUG codon. The origin of this IRES mechanism is not known. Previously, a partial fragment of a divergent dicistrovirus RNA genome, named ancient Northwest territories cripavirus (aNCV), was extracted from 700-year-old caribou feces trapped in a subarctic ice patch. Structural prediction of the aNCV IGR sequence generated a secondary structure similar to contemporary IGR IRES structures. There are, however, subtle differences including 105 nucleotides upstream of the IRES of unknown function. Using filter binding assays, we showed that the aNCV IGR IRES could bind to purified salt-washed human ribosomes and compete with a prototypical IGR IRES for ribosomes. Toeprinting analysis using primer extension pinpointed the putative start site of the aNCV IGR at a GCU alanine codon adjacent to PKI. Using a bicistronic reporter RNA, the aNCV IGR IRES can direct internal ribosome entry in vitro in a manner dependent on the integrity of the PKI domain. Lastly, we generated a chimeric virus clone by swapping the aNCV IRES into the cricket paralysis virus infectious clone. The chimeric infectious clone with an aNCV IGR IRES supported translation and virus infection. The characterization and resurrection of a functional IGR IRES from a divergent 700-year-old virus provides a historical framework in the importance of this viral translational mechanism. IMPORTANCE Internal ribosome entry sites are RNA structures that are used by some positive-sense monopartite RNA viruses to drive viral protein synthesis. The origin of internal ribosome entry sites is not known. Using biochemical approaches, we demonstrate that an RNA structure from an ancient viral genome that was discovered from a 700-year-old caribou feces trapped in subarctic ice is functionally similar to modern internal ribosome entry sites. We resurrect this ancient RNA mechanism by demonstrating that it can support virus infection in a contemporary virus clone, thus providing insights into the origin and evolution of this viral strategy.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".