RNA strand invasion activity of the Polycomb complex PRC2
Bibliographic record
Abstract
Abstract Epigenetic regulation is conveyed through information encoded by specific chromatin features. Non-canonical nucleic acid structures could in principle also convey biological information but their role(s) in epigenetic regulation is not known. Polycomb Group (PcG) proteins form memory of transient transcriptional repression events that is necessary for development. In Drosophila , PcG proteins are recruited to specific DNA sequences, Polycomb Response Elements (PREs). PREs are switchable memory elements that can exist in repressed, active, or unengaged states 1,2 . How PcG activities are targeted to PREs to maintain repressed states only in appropriate developmental contexts has been difficult to elucidate. Biochemically, PcG protein complexes modify chromatin to maintain gene repression 1,3,4 . However, PcG proteins also interact with both RNA and DNA, and RNA is implicated in the targeting of PcG function. We find that R-loops, three-stranded nucleic acid structures formed when an RNA hybridizes to its complementary DNA and displaces the other DNA strand 5 , form at many PREs in Drosophila embryos, and correlate with the repressive state. R-loops are recognized by the PcG complex PRC1 in vitro. Unexpectedly, we find that the PcG complex PRC2 has RNA strand invasion activity, which can drive formation of RNA-DNA hybrids, the key component of R-loops. Our results suggest a new mechanism for targeting PcG function through R-loop formation by PRC2 and recognition by PRC1. More generally, our findings suggest formation and recognition 6 of non-canonical nucleic acid structures as an epigenetic mechanism.
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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) | 0.002 | 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; 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".