Slipped-strand DNAs formed by long (CAG)middle dot(CTG) repeats: slipped-out repeats and slip-out junctions
Bibliographic record
Abstract
The disease-associated expansion of (CTG)*(CAG) repeats is likely to involve slipped-strand DNAs. There are two types of slipped DNAs (S-DNAs): slipped homoduplex S-DNAs are formed between two strands having the same number of repeats; and heteroduplex slipped intermediates (SI-DNAs) are formed between two strands having different numbers of repeats. We present the first characterization of S-DNAs formed by disease-relevant lengths of (CTG)*(CAG) repeats which contained all predicted components including slipped-out repeats and slip-out junctions, where two arms of the three-way junction were composed of complementary paired repeats. In S-DNAs multiple short slip-outs of CTG or CAG repeats occurred throughout the repeat tract. Strikingly, in SI-DNAs most of the excess repeats slipped-out at preferred locations along the fully base-paired Watson-Crick duplex, forming defined three-way slip-out junctions. Unexpectedly, slipped-out CAG and slipped-out CTG repeats were predominantly in the random-coil and hairpin conformations, respectively. Both the junctions and the slip-outs could be recognized by DNA metabolizing proteins: only the strand with the excess repeats was hypersensitive to cleavage by the junction-specific T7 endonuclease I, while slipped-out CAG was preferentially bound by single-strand binding protein. An excellent correlation was observed for the size of the slip-outs in S-DNAs and SI-DNAs with the size of the tract length changes observed in quiescent and proliferating tissues of affected patients-suggesting that S-DNAs and SI-DNAs are mutagenic intermediates in those tissues, occurring during error-prone DNA metabolism and replication fork errors.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.003 |
| Meta-epidemiology (narrow) | 0.001 | 0.001 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.002 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.002 | 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; both teacher heads agree on what is shown here.
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".