Lactococcus lactis ZitR Is a Zinc-Responsive Repressor Active in the Presence of Low, Nontoxic Zinc Concentrations In Vivo
Bibliographic record
Abstract
In the family Streptococcaceae, the genes encoding zinc ABC uptake systems (called zit or adc) are regulated by a coencoded MarR family member (i.e., ZitR or AdcR), whereas in the great majority of bacteria, these genes are regulated by Zur, the Fur-like zinc-responsive repressor. We studied the zit operon from Lactococcus lactis and its regulation in response to Zn(II) in vivo. zit transcription is repressed by Zn(II) in a wide concentration range starting from nontoxic micromolar levels and is derepressed at nanomolar concentrations. The level of zit promoter downregulation by environmental Zn(II) is correlated with the intracellular zinc content. The helix-turn-helix domain of ZitR is required for downregulation. In vitro, the purified protein is a dimer that complexes up to two zinc ligands per monomer and specifically binds two intact palindromic operator sites overlapping the -35 and -10 boxes of the zit promoter. DNA binding is abolished by the chelator EDTA or TPEN and fully restored by Zn(II) addition, indicating that the active repressor complexes Zn(II) with high affinity. These results suggest that derepression under starvation conditions could be an essential emergency mechanism for preserving Zn(II) homeostasis by uptake; under Zn(II)-replete conditions, the function of ZitR repression could be to help save energy rather than to avoid Zn(II) toxicity. The characterization of a MarR family zinc-responsive repressor in this report gives insight into the way Streptococcaceae efficiently adapt to Zn(II) fluctuations in their diverse ecological niches.
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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".