Biosynthesis of sulfur-containing amino acids in Streptomyces venezuelae ISP5230: roles for cystathionine β-synthase and transsulfuration b bThe GenBank accession number for the sequence reported in this paper is AF319543.
Bibliographic record
Abstract
A 0.5 kb fragment of Streptomyces venezuelae ISP5230 genomic DNA was amplified by PCR using primers based on consensus sequences of cysteine synthase isozyme A from bacteria. The deduced amino acid sequence of the PCR product resembled not only cysteine synthase sequences from prokaryotes and eukaryotes but also eukaryotic cystathionine beta-synthase sequences. Probing an Str. venezuelae genomic library with the PCR product located a hybridizing colony from which pJV207 was isolated. Sequencing and analysis of the Str. venezuelae DNA insert in pJV207 detected two ORFs. The deduced amino acid sequence of ORF1 matched both cysteine synthase and cystathionine beta-synthase sequences in GenBank, but its size favoured assignment as a cystathionine beta-synthase. ORF2 in the pJV207 insert was unrelated in function to ORF1; in its sequence the deduced product resembled acetyl-CoA transferases, but disruption of the ORF did not cause a detectable phenotypic change. Disruption of ORF1 failed to elicit cysteine auxotrophy in wild-type Str. venezuelae, but in the cys-28 auxotroph VS263 it prevented restoration of prototrophy with homocysteine or methionine supplements. The change in phenotype implicated loss of the transsulfuration activity that in the wild-type converts these supplements to cysteine. This study concludes that disruption of ORF1 inactivates a cbs gene, the product of which participates in cysteine synthesis by transsulfuration. Enzyme assays of Str. venezuelae mycelial extracts confirmed the formation of cysteine by thiolation of O-acetylserine, providing the first unambiguous detection of this activity in a streptomycete. Enzyme assays also detected cystathionine gamma-synthase, cystathionine beta-lyase and cystathionine gamma-lyase activity in the extracts and showed that the substrate for cystathionine gamma-synthase was O-succinyl-homoserine. Based on assay results, the cys-28 mutation in Str. venezuelae VS263 does not inactivate the cysteine synthase gene but impairs expression in cultures grown in minimal medium.
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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) | 0.000 | 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) | 0.001 | 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".