Heme acquisition by Shu1 requires Nbr1 and proteins of the ESCRT complex in <i>Schizosaccharomyces pombe</i>
Bibliographic record
Abstract
Summary Assimilation of heme is mediated by the cell surface protein Shu1 in Schizosaccharomyces pombe . Shu1 undergoes internalization from the cell surface to the vacuole in response to high concentrations of hemin. Here, we have identified cellular components that are involved in mediating vacuolar targeting of Shu1. Cells deficient in heme biosynthesis and lacking the polyubiquitin gene ubi4 + exhibit poor growth in the presence of exogenous hemin as a sole source of heme. Microscopic analyses of hem1 Δ shu1 Δ ubi4 Δ cells expressing a functional HA 4 ‐tagged Shu1 show that Shu1 localizes to the cell surface. Ubiquitinated Nbr1 functions as a receptor for the endosomal sorting complexes required for transport (ESCRT) that delivers cargos to the vacuole. Inactivation of nbr1 + , ESCRT‐0 hse1 + or ESCRT‐I sst6 + results in hem1 Δ cells being unable to use exogenous hemin for the growth. Using lysate preparations from hemin‐treated cells, Shu1‐Nbr1 and Shu1‐Hse1 complexes are detected by coimmunoprecipitation experiments. Further analysis by immunofluorescence microscopy shows that Shu1 is unable to reach vacuoles of hemin‐treated cells harboring a deletion for one of the following genes: ubi4 + , nbr1 + , hse1 + and sst6 + . Together, these results reveal that hemin‐mediated vacuolar targeting of Shu1 requires Ubi4‐dependent ubiquitination, the receptor Nbr1 and the ESCRT proteins Hse1 and Sst6.
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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 | 0.000 | 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 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".