Biosynthesis of the dichloroacetyl component of chloramphenicol in Streptomyces venezuelae ISP5230: genes required for halogenation
Bibliographic record
Abstract
Five ORFs were detected in a fragment from the Streptomyces venezuelae ISP5230 genomic DNA library by hybridization with a PCR product amplified from primers representing a consensus of known halogenase sequences. Sequencing and functional analyses demonstrated that ORFs 11 and 12 (but not ORFs 13-15) extended the partially characterized gene cluster for chloramphenicol (Cm) biosynthesis in the chromosome. Disruption of ORF11 (cmlK) or ORF12 (cmlS) and conjugal transfer of the insertionally inactivated genes to S. venezuelae gave mutant strains VS1111 and VS1112, each producing a similar series of Cm analogues in which unhalogenated acyl groups replaced the dichloroacetyl substituent of Cm. 1H-NMR established that the principal metabolite in the disrupted strains was the alpha-N-propionyl analogue. The sequence of CmlK implicated the protein in adenylation, and involvement in halogenation was inferred from biosynthesis of analogues by the cmlK-disrupted mutant. A role in generating the dichloroacetyl substituent was supported by partial restoration of Cm biosynthesis when a cloned copy of cmlK was introduced in trans into VS1111. Complementation of the mutant also indicated that inactivation of cmlK rather than a polar effect of the disruption on cmlS expression had interfered with dichloroacetyl biosynthesis. The deduced CmlS sequence resembled sequences of FADH2-dependent halogenases. Conjugal transfer of cmlK or cmlS into S. venezuelae cml-2, a chlorination-deficient strain with a mutation mapped genetically to the Cm biosynthesis gene cluster, did not complement the cml-2 lesion, suggesting that one or more genes in addition to cmlK and cmlS is needed to assemble the dichloroacetyl substituent. Insertional inactivation of ORF13 did not affect Cm production, and the products of ORF14 and ORF15 matched Streptomyces coelicolor A3(2) proteins lacking plausible functions in Cm biosynthesis. Thus cmlS appears to mark the downstream end of the gene cluster.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
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".