Evolution of histone H3: emergence of variants and conservation of post-translational modification sites<sup>1</sup>This article is part of Special Issue entitled Asilomar Chromatin and has undergone the Journal’s usual peer review process.
Bibliographic record
Abstract
Histone H3 proteins are highly conserved across all eukaryotes and are dynamically modified by many post-translational modifications (PTMs). Here we describe a method that defines the evolution of the family of histone H3 proteins, including the emergence of functionally distinct variants. It combines information from histone H3 protein sequences in eukaryotic species with the evolution of these species as described by the tree of life (TOL) project. This so-called TOL analysis identified the time when the few observed protein sequence changes occurred and when distinct, co-existing H3 protein variants arose. Four distinct ancient duplication events were identified where replication-coupled (RC) H3 variants diverged from replication-independent (RI) forms, like histone H3.3 in animals. These independent events occurred in ancestral lineages leading to the clades of metazoa, viridiplantae, basidiomycota, and alveolata. The proto-H3 sequence in the last eukaryotic common ancestor (LECA) was expanded to at least 133 of its 135 residues. Extreme conservation of known acetylation and methylation sites of lysines and arginines predicts that these PTMs will exist across the eukaryotic crown phyla and in protists with canonical chromatin structures. Less complete conservation was found for most serine and threonine phosphorylation sites. This study demonstrates that TOL analysis can determine the evolution of slowly evolving proteins in sequence-saturated datasets.
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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 | 0.000 | 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 teacher head, 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".