α-Anomeric Deoxynucleotides, Anoxic Products of Ionizing Radiation, Are Substrates for the Endonuclease IV-Type AP Endonucleases
Bibliographic record
Abstract
Alpha-anomeric 2'-deoxynucleosides (alphadN) are one of the products formed by ionizing radiation (IR) in DNA under anoxic conditions. Alpha-2'-deoxyadenosine (alphadA) and alpha-thymidine (alphaT) are not recognized by DNA glycosylases, and are likely removed by the alternative nucleotide incision repair (NIR) pathway. Indeed, it has been shown that alphadA is a substrate for the Escherichia coli Nfo and human Ape1 proteins. However, the repair pathway for removal of alphadA and other alphadN in yeast is unknown. Here we report that alphadA when present in DNA is recognized by the Saccharomyces cerevisiae Apn1 protein, a homologue of Nfo. Furthermore, alphaT is a substrate for Nfo and Apn1. Kinetic constants indicate that alphadA and alphaT are equally good substrates, as a tetrahydrofuranyl (THF) residue, for Nfo and Apn1. Using E. coli and S. cerevisiae cell-free extracts, we have further substantiated the role of the nfo and apn1 gene products in the repair of alphadN. Surprisingly, we found that bacteria and yeast NIR-deficient mutants are not sensitive to IR, suggesting that DNA strand breaks with terminal 3'-blocking groups rather than alphadN might contribute to cell survival. We propose that the novel substrate specificities of Nfo and Apn1 play an important role in counteracting oxidative DNA base damage.
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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) | 0.001 | 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 | 0.001 |
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".