Cryo-EM Structures of <i>Saccharolobus solfataricus</i> Initiation Complexes with Leaderless mRNAs Highlight Archaeal Features and Eukaryotic Proximity
Bibliographic record
Abstract
ABSTRACT The archaeal ribosome is of the eukaryotic type. Genomic and phylogenetic studies have indicated that TACK and Asgard, the closest relatives of eukaryotes, have ribosomes containing eukaryotic ribosomal proteins not found in other archaeal branches, eS25, eS26 and eS30. In our study, we investigated the case of Saccharolobus solfataricus , a crenarchaeon belonging to the TACK branch, which mainly uses leaderless mRNAs. We characterized the small ribosomal subunit of S. solfataricus bound to SD-leadered or leaderless mRNAs (lmRNAs). Cryo-EM structures show for the first time archaeal versions of eS25, eS26 and eS30 proteins bound to the small subunit. In addition, we identify two novel ribosomal proteins named aS33 and aS34 as well as a domain of eS6, that highlight the diversity of archaeal ribosomes. Leaderless mRNAs are bound to the small ribosomal subunit, and the 5’-triphosphate group contributes to their binding. Archaeal eS26 is in the mRNA exit channel wrapped around the 3’ end of ribosomal RNA, as it is in eukaryotes. Its position is not compatible with an SD:antiSD duplex in the mRNA exit channel. Overall, our results suggest a role of eS26 in translation regulation and possible evolutionary routes from archaeal to eukaryotic translation.
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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 | 0.001 | 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) | 0.003 | 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".