Site-directed mutagenesis studies on the uridine monophosphate binding sites of feedback inhibition in carbamoyl phosphate synthetase and effects on cytidine production by <i>Bacillus amyloliquefaciens</i>
Bibliographic record
Abstract
A major problem when pyrimidine de novo biosynthesis is used for cytidine production is the existence of many negative regulatory factors. Cytidine biosynthesis in Bacillus amyloliquefaciens proceeds via a pathway that is controlled by uridine monophosphate (UMP) through feedback inhibition of carbamoyl phosphate synthetase (CPS), the enzyme that converts CO2, NH3, and glutamine to carbamoyl phosphate. In this study, the gene carB encoding the large subunit of CPS from B. amyloliquefaciens CYT1 was site directed, and the UMP binding sites of feedback inhibition in Bam-CPS are described. The residues Thr-941, Thr-970, and Lys-986 in CPS from B. amyloliquefaciens were subjected to site-directed mutagenesis to alter UMP's feedback inhibition of CPS. To find feedback-resistant B. amyloliquefaciens, the influence of the T941F, T970A, K986I, T941F/K986I, and T941F/T970A/K986I mutations on CPS enzymatic properties was studied. The recombinant B. amyloliquefaciens with mutated T941F/K986I and T941F/T970A/K986I CPS showed a 3.7- and 5.7-fold increase, respectively, in cytidine production in comparison with the control expressing wild-type CPS, which was more suitable for further application of the cytidine synthesis. To a certain extent, the 5 mutations were found to release the enzyme from UMP inhibition and to improve B. amyloliquefaciens cytidine-producing strains.
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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 | 0.001 |
| 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 | 0.001 |
| 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".