Active self-splicing group I introns in 23S rRNA genes of hyperthermophilic bacteria, derived from introns in eukaryotic organelles
Bibliographic record
Abstract
Group I introns are common in the 23 rRNA genes of mitochondria and chloroplasts. Often, they encode "homing endonucleases," which target highly conserved gene sequences and drive interorganellar intron mobility, even across species and genus lines. Most bacterial 23S rRNA genes show these same endonuclease-sensitive target sequences. However, only two bacterial 23S rRNA genes are known to contain group I introns: that of Simkania negevensis [Everett, K. D., Kahane, S., Bush, R. M. & Friedman, M. G. (1999) J. Bacteriol. 181, 4734-4740], where the intron is not spliced and probably limits growth, and that of Coxiella burnetii [Seshadri, R., et al. (2003) Proc. Natl. Acad. Sci. USA 100, 5455-5460], where no direct evidence of splicing exists. Both bacteria are intracellular parasites and might have acquired introns from eukaryotic hosts. Here we provide direct evidence for splicing, and evolutionary evidence for mobility, of group I introns in the 23S rRNA genes of several free-living hyperthermophilic bacteria of the genus Thermotoga. These bacteria do not live closely with eukaryotes, but phylogenetic analyses suggest that their introns were also acquired from eukaryotic (probably algal) organelles. In vivo, their introns must be spliced at temperatures approaching 90 degrees C, making them the most thermostable natural ribozymes so far described. We demonstrate that at least some of these introns can also self-splice in vitro.
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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 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 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".