Functional Significance of Intermediate Cleavages in the 5′ETS of <i>Schizosaccharomyces pombe</i> pre‐rRNA
Bibliographic record
Abstract
The biosynthesis and incorporation of mature ribosomal RNAs (18S, 5.8S and 25S rRNA) into ribosomes is dependent on coordinated and interdependent processing events, acting as a “quality control mechanism”. Transcribed spacers are critical to processing and act as “biological springs” to enable the appropriate configuration of maturing termini. The pre‐rRNA 5′ external transcribed spacer (5′ ETS) of Schizosaccharomyces pombe contains structural elements critical for initiation and efficient pre‐rRNA processing. Examination of termini in the 5′ ETS region based on ligation‐mediated RT‐PCR revealed two major intermediate cleavage sites (A1 and A2) in addition to the A0 cleavage, which forms the mature 5′ end of the 18S rRNA. Mutational analyses at the A2 intermediate cleavage site indicate that this cleavage is not critical to rRNA maturation and can be eliminated. Mapping of the 5′ ETS region in cells with temperature sensitive nucleases, using RT‐PCR, refute formation of the mature 5′ end of 18S rRNA by RNase III‐like endonucleolytic cleavage across an extended hairpin. Mutational analysis around the 5′ ETS/18S rRNA junction indicate cleavage is not dependent on sequence and/or structure, but can dramatically affect rRNA yield. Additionally, mutations in U3 snoRNA or a complementary site in the 5′ 18S rRNA pseudoknot can significantly affect the 18S/25S rRNA ratio. These results raise the possibility that the 5′ end of the 18S rRNA is the result of ribozyme cleavage and that the U3 snoRNA acts as a chaperone to stabilize RNA structure. Support or Funding Information Supported by the Natural Sciences and Engineering Research Council of Canada.
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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 | 0.001 |
| 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 | 0.001 |
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".