Ku80 Binds to Human Replication Origins Prior to the Assembly of the ORC Complex
Bibliographic record
Abstract
The Ku heterodimer, an abundant nuclear protein, binds DNA replication origins in a sequence-specific manner and promotes initiation. In this study, using HCT116 Ku80+/- haplo-insufficient and Orc2(delta/-) hypomorphic cells, the order of binding of Ku and the human origin recognition complex (HsORC) was determined. The nuclear expression of Ku80 was found to be decreased by 60% in Ku80+/- cells, while its general association with chromatin was decreased by 33%. Coimmunoprecipitation studies indicated that the Ku heterodimer associates specifically with the human HsOrc-2, -3, -4, and -6 subunits. Chromatin immunoprecipitation (ChIP) experiments, using cells synchronized to late G1, showed that the association of Ku80 with the lamin B2, beta-globin, and c-myc origins in vivo was decreased by 1.5-, 2.3-, and 2.5-fold, respectively, in Ku80+/- cells. The association of HsOrc-3, -4, and -6 was consistently decreased in all three origins examined in Ku80+/- cells, while that of HsOrc-2 showed no significant variation, indicating that the HsOrc-3, -4, and -6 subunits bind to the origins after Ku80. In Orc2(delta/-) cells, the association of HsOrc-2 with the lamin B2, beta-globin, and c-myc origins was decreased by 2.8-, 4.9-, and 2.8-fold, respectively, relative to wild-type HCT116 cells. Furthermore, nascent strand abundance at these three origins was decreased by 4.5-, 2.3-, and 2.6-fold in Orc2(delta/-) relative to HCT116 cells, respectively. Interestingly, the association of Ku80 with these origins was not affected in this hypomorphic cell line, indicating that Ku and HsOrc-2 bind to origins independently of each other.
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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 | 0.001 | 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".