Purification and characterization of a novel human acidic nuclease/intra-cyclobutyl-pyrimidine-dimer-DNA phosphodiesterase
Bibliographic record
Abstract
A novel N-glycosylated, mannose-rich protein has been purified approx. 4000-fold from human liver in a seven-step procedure including ion-exchange chromatography and fractionation on concanavalin A-Sepharose, Sephadex G-75 and oligo(dT)-cellulose matrices. The molecular mass of the protein is 46 kDa when measured by gel filtration (i.e. under non-denaturing conditions) and 60 kDa by SDS/PAGE (i.e. under denaturing conditions). The protein possesses two DNA backbone-incising activities, namely, the random introduction of single-strand breaks in native DNA and the rupture of the phosphodiester linkage internal to cyclobutyl pyrimidine dimers, the major class of DNA lesions induced by solar UV rays. Both activities are optimal at pH 5.0 in vitro, although the non-specific nuclease displays appreciable activity at neutral pH, depending on the buffer composition. The protein has been named acidic nuclease/intra-cyclobutyl-pyrimidine-dimer-DNA phosphodiesterase (AN/IDP). As a nuclease, the protein 'prefers' a linear DNA structure over a covalently closed circular molecule and is more proficient at digesting single-stranded than double-stranded DNA. The polynucleotide cleavage products of the nuclease contain 5'-OH and 3'-PO(4) termini, which are refractory to direct rejoining by DNA ligases. Depending on the substrate, the nuclease activity exhibits a temperature optimum of 50 degrees C or greater, and is neither stimulated by Mg(2+) or Ca(2+) nor inhibited by Zn(2+). AN/IDP is present in human liver and in cultured human cells of both fibroblastic and lymphocytic origins. Intracellularly, the protein can be readily detected in both the cytosolic and nuclear fractions, although much more (approx. 3-fold) is found in the latter fraction. We propose that this bifunctional enzyme may be involved in both apoptotic DNA digestion and metabolism of cyclobutyl pyrimidine dimers in UV-irradiated human cells.
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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) | 0.000 | 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 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".