Effects of Salt on the Stability of a G-Quadruplex from the Human c-MYC Promoter
Bibliographic record
Abstract
In an atmosphere of potassium ions, a modified c-MYC NHE III1 sequence with two G-to-T mutations (MYC22-G14T/G23T) forms a highly stable parallel-stranded G-quadruplex. The G-quadruplex exhibits a steady increase in its melting temperature, T(M), with an increase in the concentration of the stabilizing cation K(+). On the other hand, an increase in the concentration of nonstabilizing Cs(+) or TMA(+) cations at a constant concentration of K(+) causes a sharp decline in T(M) followed by a leveling off at ∼200 mM Cs(+) or TMA(+). At 51 °C and 600 μM K(+), an increase in Cs(+) concentration from 0 to 800 mM leads to a complete unfolding of the G-quadruplex. These observations are consistent with the picture in which more counterions accumulate in the vicinity of the unfolded state of MYC22-G14T/G23T (nonspecific ion binding) than in that of the G-quadruplex state. We estimate that the unfolded state condenses one extra counterion compared to the G-quadruplex state. Taken together with our earlier results, our data suggest that sodium or potassium cations sequestered inside the central cavity stabilize the G-quadruplex conformation acting as specifically bound ligands. Nonspecifically bound (condensed) counterions may slightly stabilize, exert no influence (human telomeric G-quadruplexes), or strongly destabilize (MYC22-G14T/G23T) the G-quadruplex conformation. We offer a structural rationalization for the enhanced thermal stability of the MYC22-G14T/G23T G-quadruplex.
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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 | 0.001 |
| 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 | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| 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".