Histone H1 and the origin of protamines
Bibliographic record
Abstract
We present evidence that chordate protamines have evolved from histone H1. During the final stages of spermatogenesis, the compaction of DNA in many organisms is accomplished by the replacement of histones with a class of arginine-rich proteins called protamines. In other organisms, however, condensation of sperm DNA can occur with comparable efficiency in the presence of somatic-type histones or, alternatively, an intermediate class of proteins called protamine-like proteins. The idea that the highly specialized sperm chromosomal proteins (protamines) and somatic chromosomal proteins (histones) could be related dates back almost to the discovery of these proteins. Although this notion has frequently been revisited since that time, there has been a complete lack of supporting experimental evidence. Here we show that the emergence of protamines in chordates occurred very quickly, as a result of the conversion of a lysine-rich histone H1 to an arginine-rich protamine. We have characterized the sperm nuclear basic proteins of the tunicate Styela montereyensis, which we show consists of both a protamine and a sperm-specific histone H1 with a protamine tail. Comparison of the genes encoding these proteins to that of a sister protochordate, Ciona intestinalis, has indicated this rapid and dramatic change is most likely the result of frameshift mutations in the tail of the sperm-specific histone H1. By establishing an evolutionary link between the chromatin-condensing histone H1s of somatic tissues and the chromatin-condensing proteins of the sperm, these results provide unequivocal support to the notion that vertebrate protamines evolved from histones.
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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) | 0.001 | 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".