FB2026_01 , released March 12, 2026
FB2026_01 , released March 12, 2026
Gene: Dmel\Cbs
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General Information
Symbol
Dmel\Cbs
Species
D. melanogaster
Name
Cystathionine β-synthase
Annotation Symbol
CG1753
Feature Type
protein_coding_gene
FlyBase ID
FBgn0031148
Gene Model Status
Current
Stock Availability
13 publicly available
Enzyme Name (EC)
nitrite reductase (NO-forming) (1.7.2.1)
cystathionine beta-synthase (4.2.1.22)
Gene Summary
Cystathionine β-synthase (Cbs) encodes a cytosolic pyridoxal 5'-phosphate-dependent enzyme that catalyzes the condensation of L-homocysteine and L-serine to form L,L-cystathionine as part of L-cysteine biosynthesis (also known as the transsulfuration pathway). [Date last reviewed: 2026-02-19] (FlyBase Gene Snapshot)
All Summaries
Also Known As

dCBS

Key Links
Genomic Location
Cytogenetic map
19E7-19E7
Sequence location
Recombination map
1-65
RefSeq locus
NC_004354 REGION:21045138..21049096
Sequence
Get Decorated FASTA
Genomic Maps
Other Genome Views
The following external sites may use different assemblies or annotations than FlyBase.
NCBI
UCSC
Ensembl
PopFly
Function
Gene Ontology (GO) Annotations (10 terms)
Molecular Function (2 terms)
Terms Based on Experimental Evidence (1 term)
CV Term
Evidence
References
enables cystathionine beta-synthase activity
inferred from direct assay
(Kabil et al., 2011)
Terms Based on Predictions or Assertions (2 terms)
CV Term
Evidence
References
enables cystathionine beta-synthase activity
inferred from biological aspect of ancestor with PANTHER:PTN000034107
(GO Reference Genome Project, 2011-)
inferred from electronic annotation with InterPro:IPR005857
(InterPro Project Members, 2004-)
enables nitrite reductase (NO-forming) activity
inferred from sequence or structural similarity with UniProtKB:P35520
(Gene Ontology Curators, 2002-)
Biological Process (7 terms)
Terms Based on Experimental Evidence (4 terms)
CV Term
Evidence
References
involved_in hydrogen sulfide biosynthetic process
inferred from mutant phenotype
(Shilova et al., 2025)
involved_in L-cysteine biosynthetic process
inferred from mutant phenotype
(Jouandin et al., 2022)
involved_in response to endoplasmic reticulum stress
inferred from high throughput mutant phenotype
(Chow et al., 2013)
involved_in transsulfuration
inferred from mutant phenotype
(Kabil et al., 2011)
Terms Based on Predictions or Assertions (3 terms)
CV Term
Evidence
References
involved_in homocysteine metabolic process
inferred from sequence or structural similarity with UniProtKB:P35520
(Gene Ontology Curators, 2002-)
involved_in L-cysteine biosynthetic process from L-serine
inferred from electronic annotation with InterPro:IPR001216
(InterPro Project Members, 2004-)
involved_in L-cysteine biosynthetic process via L-cystathionine
inferred from biological aspect of ancestor with PANTHER:PTN000034107
(GO Reference Genome Project, 2011-)
inferred from electronic annotation with InterPro:IPR005857
(InterPro Project Members, 2004-)
Cellular Component (1 term)
Terms Based on Experimental Evidence (0 terms)
Terms Based on Predictions or Assertions (1 term)
CV Term
Evidence
References
is_active_in cytoplasm
inferred from biological aspect of ancestor with PANTHER:PTN000034104
(GO Reference Genome Project, 2011-)
located_in cytoplasm
inferred from electronic annotation with InterPro:IPR005857
(InterPro Project Members, 2004-)
Gene Group (FlyBase)
Pathway (FlyBase)
Protein Family (UniProt)
-
Protein Signatures (InterPro)
Catalytic Activity (EC/Rhea)
nitrite reductase (NO-forming) activity
nitric oxide + Fe(III)-[cytochrome c] + H2O = Fe(II)-[cytochrome c] + nitrite + 2 H(+) (1.7.2.1)
RHEA 15233: cystathionine beta-synthase activity
L-homocysteine + L-serine = L,L-cystathionine + H2O (4.2.1.22)
RHEA 10112:
Summaries
Gene Snapshot
Cystathionine β-synthase (Cbs) encodes a cytosolic pyridoxal 5'-phosphate-dependent enzyme that catalyzes the condensation of L-homocysteine and L-serine to form L,L-cystathionine as part of L-cysteine biosynthesis (also known as the transsulfuration pathway). [Date last reviewed: 2026-02-19]
Gene Group (FlyBase)
UNCLASSIFIED HYDRO-LYASES -
This group comprises hydro-lyases that do not classify under other groups in FlyBase.
OTHER NITROGENOUS GROUP OXIDOREDUCTASES -
Nitrogenous group oxidoreductases include dehydrogenases that oxidize nitrogenous groups, excluding NH and NH2 groups, with the reduction of hydrogen or electron acceptor.
Pathway (FlyBase)
L-CYSTEINE BIOSYNTHESIS -
L-cysteine biosynthesis, also known as the transsulfuration pathway, occurs in the cytosol and converts L-homocysteine, a metabolite derived from L-methionine metabolism, to L-cysteine. Besides its role in protein biosynthesis, L-cysteine is also a precursor for glutathione, taurine, hypotaurine and hydrogen sulfide (H2S) production. It is involved in the synthesis of Mo-molybdopterin cofactor, Iron-Sulfur (Fe-S) cluster assembly and coenzyme A. (Adapted from PMID:31460700 and PMID: 29530337.)
Gene Model and Products
Number of Transcripts
3
Number of Unique Polypeptides
1

Please see the JBrowse view of Dmel\Cbs for information on other features

To submit a correction to a gene model please use the Contact FlyBase form

Protein Domains (via Pfam)
Isoform displayed:
Pfam protein domains
InterPro name
classification
start
end
Protein Domains (via SMART)
Isoform displayed:
SMART protein domains
InterPro name
classification
start
end
Structure
Protein 3D structure   (Predicted by AlphaFold)   (AlphaFold entry Q9VRD9)

If you don't see a structure in the viewer, refresh your browser.
Model Confidence:
  • Very high (pLDDT > 90)
  • Confident (90 > pLDDT > 70)
  • Low (70 > pLDDT > 50)
  • Very low (pLDDT < 50)

AlphaFold produces a per-residue confidence score (pLDDT) between 0 and 100. Some regions with low pLDDT may be unstructured in isolation.

Experimentally Determined Structures
Crossreferences
PDB - An information portal to biological macromolecular structures
Comments on Gene Model

Gene model reviewed during 5.50

Transcript Data
Annotated Transcripts
Name
FlyBase ID
RefSeq ID
Length (nt)
Assoc. CDS (aa)
Cbs-RA
FBtr0077244
NM_134580
1911
522
Cbs-RB
FBtr0077245
NM_167726
1990
522
Cbs-RC
FBtr0340437
NM_001298579
1788
522
Additional Transcript Data and Comments
Reported size (kB)
Comments
External Data
Crossreferences
Polypeptide Data
Annotated Polypeptides
Name
FlyBase ID
Predicted MW (kDa)
Length (aa)
Theoretical pI
UniProt
RefSeq ID
GenBank
Cbs-PA
FBpp0076937
56.9
522
7.07
Q9VRD9
NP_608424
AAF50862
Cbs-PB
FBpp0076938
56.9
522
7.07
Q9VRD9
NP_728384
AAF50863
Cbs-PC
FBpp0309380
56.9
522
7.07
Q9VRD9
NP_001285508
AHN59978
Polypeptides with Identical Sequences

The group(s) of polypeptides indicated below share identical sequence to each other.

522 aa isoforms: Cbs-PA, Cbs-PB, Cbs-PC
Additional Polypeptide Data and Comments
Reported size (kDa)
Comments
External Data
Crossreferences
InterPro - A database of protein families, domains and functional sites
PDB - An information portal to biological macromolecular structures
Linkouts
Sequences Consistent with the Gene Model
Mapped Features

Click to get a list of regulatory features (enhancers, TFBS, etc.) and gene disruptions (point mutations, indels, etc.) within or overlapping Dmel\Cbs using the Feature Mapper tool.

External Data
Crossreferences
Eukaryotic Promoter Database - A collection of databases of experimentally validated promoters for selected model organisms.
Linkouts
Expression Data
Testis-specificity index

The testis specificity index was calculated from modENCODE tissue expression data by Vedelek et al., 2018 to indicate the degree of testis enrichment compared to other tissues. Scores range from -2.52 (underrepresented) to 5.2 (very high testis bias).

-0.46

Transcript Expression
in situ
Stage
Tissue/Position (including subcellular localization)
Reference
embryonic stage 1 -- 3
organism

Comment: maternally deposited

(Fisher et al., 2012)
embryonic stage 4 -- 6
organism
(Fisher et al., 2012)
embryonic stage 13 -- 16
embryonic midgut chamber
(Fisher et al., 2012)
embryonic/larval midgut
(Fisher et al., 2012)
gastric caecum
(Fisher et al., 2012)
Additional Descriptive Data
Marker for
 
Subcellular Localization
CV Term
Polypeptide Expression
Additional Descriptive Data
Marker for
 
Subcellular Localization
CV Term
Evidence
References
Expression Deduced from Reporters
High-Throughput Expression Data
Associated Tools

JBrowse - Visual display of RNA-Seq signals

View Dmel\Cbs in JBrowse
RNA-Seq by Region - Search RNA-Seq expression levels by exon or genomic region
Bulk Downloads
RNA-Seq RPKM values for all genes
Reference
See Gelbart and Emmert, 2013 for analysis details and data files for all genes.
Developmental Proteome: Life Cycle
Developmental Proteome: Embryogenesis
External Data and Images
Linkouts
BDGP expression data - Patterns of gene expression in Drosophila embryogenesis
DRscDB - A single-cell RNA-seq resource for data mining and data comparison across species
EMBL-EBI Single Cell Expression Atlas - Single cell expression across species
FlyAtlas - Adult expression by tissue, using Affymetrix Dros2 array
FlyAtlas2 - A Drosophila melanogaster expression atlas with RNA-Seq, miRNA-Seq and sex-specific data
Fly-FISH - A database of Drosophila embryo and larvae mRNA localization patterns
Flygut - An atlas of the Drosophila adult midgut
Images
FlyExpress - Embryonic expression images (BDGP data)
  • Stages(s) 1-3
  • Stages(s) 4-6
  • Stages(s) 13-16
FlyBase Wiki
Image Based Resources
Alleles, Insertions, Transgenic Constructs, and Aberrations
Classical and Insertion Alleles ( 9 )
For All Classical and Insertion Alleles Show
 
Other relevant insertions
Transgenic Constructs ( 11 )
For All Alleles Carried on Transgenic Constructs Show
Transgenic constructs containing/affecting coding region of Cbs
Transgenic constructs containing regulatory region of Cbs
Aberrations (Deficiencies and Duplications) ( 0 )
Variants
Variant Molecular Consequences
Alleles Representing Disease-Implicated Variants
Phenotypes
Orthologs
Downloads
Download All DIOPT Orthologs
Human Orthologs (via DIOPT v9.1)
Species\Gene Symbol
Score
Best Score
Best Reverse Score
Source
Compara
Domainoid
eggNOG
Hieranoid
Homologene
Inparanoid
OMA
OrthoDB
OrthoFinder
OrthoInspector
orthoMCL
Panther
Phylome
SonicParanoid
Alignment
Complementation?
Transgene?
Homo sapiens (Human) (5)
Hsap\CBS
14 of 14
Yes
Yes
1  
Hsap\CBSL
14 of 14
Yes
Yes
Hsap\SDS
1 of 14
No
No
Hsap\SDSL
1 of 14
No
No
Hsap\SRR
1 of 14
No
No
1  
Model Organism Orthologs (via DIOPT v9.1)
Species\Gene Symbol
Score
Best Score
Best Reverse Score
Source
Compara
Domainoid
eggNOG
Hieranoid
Homologene
Inparanoid
OMA
OrthoDB
OrthoFinder
OrthoInspector
orthoMCL
Panther
Phylome
SonicParanoid
Alignment
Complementation?
Transgene?
Rattus norvegicus (Norway rat) (4)
Rnor\Cbs
13 of 14
Yes
Yes
Rnor\Sdsl
1 of 14
No
No
Rnor\Sds
1 of 14
No
Yes
Rnor\Srr
1 of 14
No
No
Mus musculus (laboratory mouse) (4)
Mmus\Cbs
13 of 14
Yes
Yes
Mmus\Sdsl
1 of 14
No
No
Mmus\Sds
1 of 14
No
No
Mmus\Srr
1 of 14
No
No
Xenopus tropicalis (Western clawed frog) (3)
Xtro\cbs
7 of 13
Yes
Yes
Xtro\srr
1 of 13
No
No
Xtro\XB5822195
1 of 13
No
No
Danio rerio (Zebrafish) (5)
Drer\cbsa
14 of 14
Yes
Yes
Drer\cbsb
13 of 14
No
Yes
Drer\sdsl
1 of 14
No
Yes
Drer\si:ch73-263o4.3
1 of 14
No
No
Drer\srr
1 of 14
No
No
Caenorhabditis elegans (Nematode, roundworm) (13)
Cele\cbs-2
10 of 14
Yes
Yes
Cele\cbs-1
9 of 14
No
Yes
Cele\cysl-1
9 of 14
No
Yes
Cele\cysl-2
9 of 14
No
Yes
Cele\cysl-4
9 of 14
No
Yes
Cele\cysl-3
8 of 14
No
Yes
Cele\F59A7.7
4 of 14
No
Yes
Cele\F01D4.8
3 of 14
No
Yes
Cele\F13B12.4
3 of 14
No
Yes
Cele\T25D3.3
2 of 14
No
Yes
Cele\K01C8.1
1 of 14
No
No
Cele\serr-1
1 of 14
No
No
Cele\Y51H7C.9
1 of 14
No
No
Anopheles gambiae (African malaria mosquito) (3)
Agam\AgaP_AGAP000162
12 of 12
Yes
Yes
Agam\AgaP_AGAP012897
7 of 12
No
Yes
Agam\AgaP_AGAP003571
1 of 12
No
No
Arabidopsis thaliana (thale-cress) (16)
Atha\CYSC1
10 of 13
Yes
Yes
Atha\CYSD1
10 of 13
Yes
Yes
Atha\CYSD2
10 of 13
Yes
Yes
Atha\DES1
10 of 13
Yes
Yes
Atha\OASA1
10 of 13
Yes
Yes
Atha\OASB
10 of 13
Yes
Yes
Atha\OASC
10 of 13
Yes
Yes
Atha\CS26
9 of 13
No
Yes
Atha\OASA2
8 of 13
No
Yes
Atha\AT1G55880
5 of 13
No
Yes
Atha\MTO2
1 of 13
No
Yes
Atha\OMR1
1 of 13
No
No
Atha\SR
1 of 13
No
No
Atha\TSB1
1 of 13
No
Yes
Atha\TSB2
1 of 13
No
Yes
Atha\TSBtype2
1 of 13
No
Yes
Saccharomyces cerevisiae (Brewer's yeast) (5)
Scer\CYS4
13 of 13
Yes
Yes
Scer\MCY1
4 of 13
No
Yes
Scer\CHA1
1 of 13
No
No
Scer\ILV1
1 of 13
No
No
Scer\SRY1
1 of 13
No
No
Schizosaccharomyces pombe (Fission yeast) (4)
Spom\cys11
8 of 12
Yes
Yes
Spom\cys12
7 of 12
No
Yes
Spom\SPBC1677.03c
1 of 12
No
No
Spom\SPCC320.14
1 of 12
No
No
Escherichia coli (enterobacterium) (5)
Ecol\cysK
8 of 11
Yes
Yes
Ecol\cysM
8 of 11
Yes
Yes
Ecol\ilvA
1 of 11
No
No
Ecol\tdcB
1 of 11
No
No
Ecol\ygeX
1 of 11
No
Yes
Other Organism Orthologs (via OrthoDB)
Data provided directly from OrthoDB:Cbs. Refer to their site for version information.
Paralogs
Downloads
Download All DIOPT Paralogs
Paralogs (via DIOPT v9.1)
Gene Symbol
Score
Source
Compara
Domainoid
eggNOG
Homologene
Inparanoid
OMA
OrthoDB
OrthoFinder
OrthoInspector
orthoMCL
Panther
Phylome
SonicParanoid
Alignment
Drosophila melanogaster (Fruit fly) (1)
Srr
2 of 13
Human Disease Associations
FlyBase Human Disease Model Reports
Disease Ontology (DO) Annotations
Models Based on Experimental Evidence ( 3 )
Potential Models Based on Orthology ( 1 )
Human Ortholog
Disease
Evidence
References
CBS; cystathionine beta-synthase
model of  homocystinuria
IEA
(FlyBase, 2019-)
Modifiers Based on Experimental Evidence ( 0 )
Allele
Disease
Interaction
References
Disease Associations of Human Orthologs (via DIOPT v9.1 and OMIM)
Note that ortholog calls supported by only 1 or 2 algorithms (DIOPT score < 3) are not shown.
Homo sapiens (Human)
Gene name
Score
OMIM
OMIM Phenotype
DO term
Complementation?
Transgene?
CBS; cystathionine beta-synthase
14 of 14
613381
 
Hsap\CBSL
14 of 14
      Functional Complementation Data
      Functional complementation data is computed by FlyBase using a combination of the orthology data obtained from DIOPT and OrthoDB and the allele-level genetic interaction data curated from the literature.
      Interactions
      Summary of Physical Interactions
      Interaction Browsers
      Summary of Genetic Interactions
      Interaction Browsers
      Starting gene(s)
      Interaction type
      Interacting gene(s)
      Reference
      Starting gene(s)
      Interaction type
      Interacting gene(s)
      Reference
      External Data
      Linkouts
      BioGRID - A database of protein and genetic interactions.
      DroID - A comprehensive database of gene and protein interactions.
      MIST (protein-protein) - An integrated Molecular Interaction Database
      Pathways
      Signaling Pathways (FlyBase)
      Metabolic Pathways
      FlyBase
      L-CYSTEINE BIOSYNTHESIS
      External Links
      FlyCyc Pathways - Pathways from a BioCyc PGDB for Dmel
      KEGG Metabolic Pathways - A collection of manually drawn metabolic pathway maps representing knowledge of molecular interaction, reaction and relation networks.
      Reactome Metabolic Pathways - An open-source, open access, manually curated and peer-reviewed metabolic pathway database.
      External Data
      Linkouts
      KEGG Pathways - A collection of manually drawn pathway maps representing knowledge of molecular interaction, reaction and relation networks.
      Reactome - An open-source, open access, manually curated and peer-reviewed pathway database.
      Class of Gene
      Genomic Location and Detailed Mapping Data
      Chromosome (arm)
      X
      Recombination map
      1-65
      Cytogenetic map
      19E7-19E7
      Sequence location
      FlyBase Computed Cytological Location
      Cytogenetic map
      Evidence for location
      19E7-19E7
      Limits computationally determined from genome sequence between P{EP}CG1702EP1525 and P{EP}EP1465&P{EP}CG1486EP1192
      Experimentally Determined Cytological Location
      Cytogenetic map
      Notes
      References
      Experimentally Determined Recombination Data
      Location

      1-65

      (FlyBase, 2016)

      1-65.7

      (Comeron et al., 2012)
      Left of (cM)
      Right of (cM)
      Notes
      Stocks and Reagents
      Stocks (13)
      Genomic Clones (14)
       

      Please Note FlyBase no longer curates genomic clone accessions so this list may not be complete

      cDNA Clones (70)
       

      Please Note This section lists cDNAs and ESTs that fall within the genomic extent of the gene model, which may include cDNAs and ESTs of genes within introns, or of overlapping genes. Please see JBrowse for alignment of the cDNAs and ESTs to the gene model.

      cDNA clones, fully sequenced
      BDGP DGC clones
      Other clones
        Drosophila Genomics Resource Center cDNA clones

        For each fully sequenced cDNA the DGRC maintains various forms of the cDNA (e.g tagged or untagged) in several different host vectors for subsequent cloning and expression in Drosophila and Drosophila cell lines.

        cDNA Clones, End Sequenced (ESTs)
        BDGP DGC clones
        Other clones
        RNAi and Array Information
        Linkouts
        DRSC - Results frm RNAi screens
        Antibody Information
        Laboratory Generated Antibodies
         
        Commercially Available Antibodies
         
        Cell Line Information
        Publicly Available Cell Lines
         
          Other Stable Cell Lines
           
            Other Comments

            Nonsense-mediated mRNA decay (NMD) down-regulates a distinct splice isoform(s) of this gene.

            (Hansen et al., 2009)
            Relationship to Other Genes
            Source for database merge of
            Additional comments
            Nomenclature History
            Source for database identify of

            Source for identity of: Cbs CG1753

            (Kabil et al., 2011)
            Nomenclature comments
            Etymology
            Synonyms and Secondary IDs (13)
            Datasets (0)
            Study focus (0)
            Experimental Role
            Project
            Project Type
            Title
            Study result (0)
            Result
            Result Type
            Title
            External Crossreferences and Linkouts ( 60 )
            Sequence Crossreferences
            NCBI Gene - Gene integrates information from a wide range of species. A record may include nomenclature, Reference Sequences (RefSeqs), maps, pathways, variations, phenotypes, and links to genome-, phenotype-, and locus-specific resources worldwide.
            GenBank Nucleotide - A collection of sequences from several sources, including GenBank, RefSeq, TPA, and PDB.
            GenBank Protein - A collection of sequences from several sources, including translations from annotated coding regions in GenBank, RefSeq and TPA, as well as records from SwissProt, PIR, PRF, and PDB.
            RefSeq - A comprehensive, integrated, non-redundant, well-annotated set of reference sequences including genomic, transcript, and protein.
            UniProt/GCRP - The gene-centric reference proteome (GCRP) provides a 1:1 mapping between genes and UniProt accessions in which a single 'canonical' isoform represents the product(s) of each protein-coding gene.
            UniProt/TrEMBL - Automatically annotated and unreviewed records of protein sequence and functional information
            Other crossreferences
            AlphaFold DB - AlphaFold provides open access to protein structure predictions for the human proteome and other key proteins of interest, to accelerate scientific research.
            BDGP expression data - Patterns of gene expression in Drosophila embryogenesis
            DRscDB - A single-cell RNA-seq resource for data mining and data comparison across species
            EMBL-EBI Single Cell Expression Atlas - Single cell expression across species
            FlyAtlas2 - A Drosophila melanogaster expression atlas with RNA-Seq, miRNA-Seq and sex-specific data
            FlyMine - An integrated database for Drosophila genomics
            InterPro - A database of protein families, domains and functional sites
            KEGG Genes - Molecular building blocks of life in the genomic space.
            MARRVEL_MODEL - MARRVEL (model organism gene)
            PDB - An information portal to biological macromolecular structures
            Linkouts
            BioGRID - A database of protein and genetic interactions.
            Drosophila Genomics Resource Center - Drosophila Genomics Resource Center (DGRC) cDNA clones
            DroID - A comprehensive database of gene and protein interactions.
            DRSC - Results frm RNAi screens
            Eukaryotic Promoter Database - A collection of databases of experimentally validated promoters for selected model organisms.
            FlyAtlas - Adult expression by tissue, using Affymetrix Dros2 array
            FlyCyc Genes - Genes from a BioCyc PGDB for Dmel
            FlyCyc Pathways - Pathways from a BioCyc PGDB for Dmel
            Fly-FISH - A database of Drosophila embryo and larvae mRNA localization patterns
            Flygut - An atlas of the Drosophila adult midgut
            FlyMet - A comprehensive tissue-specific metabolomics resource for Drosophila.
            iBeetle-Base - RNAi phenotypes in the red flour beetle (Tribolium castaneum)
            KEGG Metabolic Pathways - A collection of manually drawn metabolic pathway maps representing knowledge of molecular interaction, reaction and relation networks.
            KEGG Pathways - A collection of manually drawn pathway maps representing knowledge of molecular interaction, reaction and relation networks.
            MIST (protein-protein) - An integrated Molecular Interaction Database
            Reactome - An open-source, open access, manually curated and peer-reviewed pathway database.
            Reactome Metabolic Pathways - An open-source, open access, manually curated and peer-reviewed metabolic pathway database.
            References (70)