FB2026_01 , released March 12, 2026
FB2026_01 , released March 12, 2026
Gene: Dmel\Polr1B
Open Close
General Information
Symbol
Dmel\Polr1B
Species
D. melanogaster
Name
RNA polymerase I subunit B
Annotation Symbol
CG4033
Feature Type
protein_coding_gene
FlyBase ID
FBgn0003278
Gene Model Status
Current
Stock Availability
7 publicly available
Enzyme Name (EC)
DNA-directed RNA polymerase (2.7.7.6)
Gene Summary
DNA-dependent RNA polymerase catalyzes the transcription of DNA into RNA using the four ribonucleoside triphosphates as substrates. Second largest core component of RNA polymerase I which synthesizes ribosomal RNA precursors. Proposed to contribute to the polymerase catalytic activity and forms the polymerase active center together with the largest subunit. Pol I is composed of mobile elements and RPA2 is part of the core element with the central large cleft and probably a clamp element that moves to open and close the cleft (By similarity). (UniProt, P20028)
Contribute a Gene Snapshot for this gene.
All Summaries
Also Known As

RpI135, Rpl135, DmRP135, RNA polymerase I

Key Links
Genomic Location
Cytogenetic map
21C2-21C2
Sequence location
Recombination map
2-0.7
RefSeq locus
NT_033779 REGION:404285..407969
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 (8 terms)
Molecular Function (3 terms)
Biological Process (3 terms)
Terms Based on Experimental Evidence (0 terms)
Terms Based on Predictions or Assertions (3 terms)
CV Term
Evidence
References
involved_in DNA-templated transcription
(InterPro Project Members, 2004-)
involved_in transcription by RNA polymerase I
inferred from sequence or structural similarity with UniProtKB:P22138
(Gene Ontology Curators, 2002-)
involved_in transcription elongation by RNA polymerase I
inferred from biological aspect of ancestor with PANTHER:PTN000465942
(GO Reference Genome Project, 2011-)
Cellular Component (2 terms)
Terms Based on Experimental Evidence (0 terms)
Terms Based on Predictions or Assertions (2 terms)
CV Term
Evidence
References
located_in nucleus
inferred from electronic annotation with InterPro:IPR009674
(InterPro Project Members, 2004-)
part_of RNA polymerase I complex
inferred from biological aspect of ancestor with PANTHER:PTN000465942
(GO Reference Genome Project, 2011-)
inferred from sequence or structural similarity with UniProtKB:P22138
(Gene Ontology Curators, 2002-)
Gene Group (FlyBase)
Protein Family (UniProt)
Belongs to the RNA polymerase beta chain family. (P20028)
Protein Signatures (InterPro)
Catalytic Activity (EC/Rhea)
DNA-directed RNA polymerase activity
RNA(n) + a ribonucleoside 5'-triphosphate = RNA(n+1) + diphosphate (2.7.7.6)
Summaries
Gene Group (FlyBase)
RNA POLYMERASE I -
RNA polymerase I (RNAP I) synthesizes the ribosomal RNA precursor that is processed into most ribosomal RNAs (rRNAs). It comprises 12-14 subunits (12 in D. melanogaster), ten of which form a structurally conserved catalytic core with additional subunits located on the periphery. Notably, five RNAP I subunits are shared with the other two nuclear RNAPs, and two others are shared between RNAPs I and III. (Adapted from FBrf0247389.)
RNA POLYMERASE CATALYTIC SUBUNITS -
DNA-directed RNA polymerases (RNAPs) catalyze the synthesis of RNA from DNA templates. Nuclear DNA is transcribed by three different multi-subunit polymerases, RNAPs I, II and III, which synthesize mRNAs, rRNAs, tRNAs and other non-coding RNAs. Although composed of between 12-17 subunits, all three nuclear RNAPs contain a ten-subunit catalytic core. Mitochondrial RNA is synthesized by a single subunit RNA polymerase. DNA primases are a class of RNA polymerases that catalyse the synthesis of short RNA primers that are extended by DNA polymerases during DNA replication. (Adapted from PMID:22365827 and PMID:19540940.)
Protein Function (UniProtKB)
DNA-dependent RNA polymerase catalyzes the transcription of DNA into RNA using the four ribonucleoside triphosphates as substrates. Second largest core component of RNA polymerase I which synthesizes ribosomal RNA precursors. Proposed to contribute to the polymerase catalytic activity and forms the polymerase active center together with the largest subunit. Pol I is composed of mobile elements and RPA2 is part of the core element with the central large cleft and probably a clamp element that moves to open and close the cleft (By similarity).
(UniProt, P20028)
Gene Model and Products
Number of Transcripts
1
Number of Unique Polypeptides
1

Please see the JBrowse view of Dmel\Polr1B 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 P20028)

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
Comments on Gene Model

Gene model reviewed during 5.52

Transcript Data
Annotated Transcripts
Name
FlyBase ID
RefSeq ID
Length (nt)
Assoc. CDS (aa)
Polr1B-RA
FBtr0078054
NM_057360
3564
1129
Additional Transcript Data and Comments
Reported size (kB)

3.6 (northern blot)

(Kontermann et al., 1989)
Comments
External Data
Crossreferences
Polypeptide Data
Annotated Polypeptides
Name
FlyBase ID
Predicted MW (kDa)
Length (aa)
Theoretical pI
UniProt
RefSeq ID
GenBank
Polr1B-PA
FBpp0077714
128.4
1129
8.53
P20028
NP_476708
AAF51503
Polypeptides with Identical Sequences

There is only one protein coding transcript and one polypeptide associated with this gene

Additional Polypeptide Data and Comments
Reported size (kDa)

1129 (aa)

(Kontermann et al., 1989)
Comments
External Data
Subunit Structure (UniProtKB)

Component of the RNA polymerase I (Pol I) complex consisting of at least 13 subunits.

(UniProt, P20028)
Crossreferences
InterPro - A database of protein families, domains and functional sites
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\Polr1B 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).

-0.62

Transcript Expression
Polypeptide Expression
mass spectroscopy
Stage
Tissue/Position (including subcellular localization)
Reference
adult stage
adult head
(Aradska et al., 2015)
day 5 of adulthood | male -- day 7 of adulthood | male
spermatozoon
(Wasbrough et al., 2010)
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\Polr1B 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) 7-8
  • Stages(s) 11-12
  • Stages(s) 13-16
FlyBase Wiki
Image Based Resources
Alleles, Insertions, Transgenic Constructs, and Aberrations
Classical and Insertion Alleles ( 6 )
For All Classical and Insertion Alleles Show
 
Other relevant insertions
Transgenic Constructs ( 5 )
For All Alleles Carried on Transgenic Constructs Show
Transgenic constructs containing/affecting coding region of Polr1B
Transgenic constructs containing regulatory region of Polr1B
Aberrations (Deficiencies and Duplications) ( 3 )
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) (3)
Hsap\POLR1B
14 of 14
Yes
Yes
1  
Hsap\POLR3B
4 of 14
No
No
Hsap\POLR2B
3 of 14
No
No
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) (3)
Rnor\Polr1b
14 of 14
Yes
Yes
Rnor\Polr2b
4 of 14
No
No
Rnor\Polr3b
4 of 14
No
No
Mus musculus (laboratory mouse) (3)
Mmus\Polr1b
13 of 14
Yes
Yes
Mmus\Polr2b
4 of 14
No
No
Mmus\Polr3b
4 of 14
No
No
Xenopus tropicalis (Western clawed frog) (6)
Xtro\polr1b
11 of 13
Yes
Yes
Xtro\polr2b
3 of 13
No
No
Xtro\polr3b
2 of 13
No
No
Xtro\gdnf
1 of 13
No
Yes
Xtro\kiaa1191
1 of 13
No
Yes
Xtro\rab14
1 of 13
No
No
Danio rerio (Zebrafish) (4)
Drer\polr1b
14 of 14
Yes
Yes
Drer\polr3b
4 of 14
No
No
Drer\polr2b
3 of 14
No
No
Drer\LOC100537264
2 of 14
No
No
Caenorhabditis elegans (Nematode, roundworm) (3)
Cele\rpoa-2
14 of 14
Yes
Yes
Cele\rpb-2
4 of 14
No
No
Cele\rpc-2
4 of 14
No
No
Anopheles gambiae (African malaria mosquito) (3)
Agam\AgaP_AGAP009539
12 of 12
Yes
Yes
Agam\AgaP_AGAP003648
4 of 12
No
No
Agam\AgaP_AGAP008151
4 of 12
No
No
Arabidopsis thaliana (thale-cress) (6)
Atha\NRPA2
13 of 13
Yes
Yes
Atha\NRPB2
4 of 13
No
No
Atha\NRPC2
4 of 13
No
No
Atha\NRPD2A
4 of 13
No
No
Atha\NRPD2B
4 of 13
No
No
Atha\rpoB
2 of 13
No
No
Saccharomyces cerevisiae (Brewer's yeast) (3)
Scer\RPA135
13 of 13
Yes
Yes
Scer\RET1
3 of 13
No
No
Scer\RPB2
3 of 13
No
No
Schizosaccharomyces pombe (Fission yeast) (3)
Spom\rpa2
12 of 12
Yes
Yes
Spom\rpb2
3 of 12
No
No
Spom\rpc2
3 of 12
No
No
Escherichia coli (enterobacterium) (1)
Ecol\rpoB
5 of 11
Yes
No
Other Organism Orthologs (via OrthoDB)
Data provided directly from OrthoDB:Polr1B. 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) (2)
Polr2B
8 of 13
Polr3B
8 of 13
Human Disease Associations
FlyBase Human Disease Model Reports
    Disease Ontology (DO) Annotations
    Models Based on Experimental Evidence ( 0 )
    Allele
    Disease
    Evidence
    References
    Potential Models Based on Orthology ( 1 )
    Human Ortholog
    Disease
    Evidence
    References
    POLR1B; RNA polymerase I subunit B
    model of  Treacher Collins syndrome 4
    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?
    POLR1B; RNA polymerase I subunit B
    14 of 14
    602000
     
    POLR3B; RNA polymerase III subunit B
    4 of 14
    614366
    POLR2B; RNA polymerase II subunit B
    3 of 14
    180661
        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
        Summary of Genetic Interactions
        Interaction Browsers
        View in FlyBase Interactions Browser   View in MIST tool (external link)
        Please look at the allele data for full details of the genetic interactions
        Starting gene(s)
        Interaction type
        Interacting gene(s)
        Reference
        Polr1B
        suppressible
        RpS13
        (Grewal et al., 2005)
        Starting gene(s)
        Interaction type
        Interacting gene(s)
        Reference
        Ras85D
        suppressible
        Polr1B
        (Gaur et al., 2013)
        External Data
        Subunit Structure (UniProtKB)
        Component of the RNA polymerase I (Pol I) complex consisting of at least 13 subunits.
        (UniProt, P20028 )
        Linkouts
        DroID - A comprehensive database of gene and protein interactions.
        MIST (protein-protein) - An integrated Molecular Interaction Database
        Pathways
        Signaling Pathways (FlyBase)
        Metabolic Pathways
        FlyBase
        External Links
        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)
        2L
        Recombination map
        2-0.7
        Cytogenetic map
        21C2-21C2
        Sequence location
        FlyBase Computed Cytological Location
        Cytogenetic map
        Evidence for location
        21C2-21C2
        Limits computationally determined from genome sequence between P{lacW}U2af38k14504 and P{lacW}RpI135k16513&P{lacW}ebik16213
        Experimentally Determined Cytological Location
        Cytogenetic map
        Notes
        References
        21C1-21C2
        (determined by in situ hybridisation)
        (Spradling et al., 1999)
        21C1-21C2
        (BDGP Project Members, 1994-1999)
        21C-21C
        (determined by in situ hybridisation)
        (Kontermann et al., 1989)
        Experimentally Determined Recombination Data
        Location

        2-0.7

        (FlyBase, 2016)

        2-0.0

        (Comeron et al., 2012)
        Left of (cM)
        Right of (cM)
        Notes
        Stocks and Reagents
        Stocks (7)
        Genomic Clones (18)
        cDNA Clones (22)
         

        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
           

          polyclonal

          (Seifarth et al., 1991, Kontermann et al., 1989)
          Commercially Available Antibodies
           
          Cell Line Information
          Publicly Available Cell Lines
           
            Other Stable Cell Lines
             
              Other Comments

              dsRNA made from templates generated with primers directed against this gene in combination with dsRNA against gig results in suppression of the final average cell size, with it being closer to the control average cell size, rather than the average cell size resulting from knockdown of the candidate gene alone.

              (Guertin et al., 2006)

              In a sample of 79 genes with multiple introns, 33 showed significant heterogeneity in G+C content among introns of the same gene and significant positive correspondence between the intron and the third codon position G+C content within genes. These results are consistent with selection adding against preferred codons at the start of genes.

              (Kliman and Eyre-Walker, 1998)

              Based on biochemical evidence, it has been shown that RpI135 encodes the second largest subunit of RNA polymerase I, and not the equivalent subunit of RNA polymerase III, as previously reported (FBrf0050568).

              (Seifarth et al., 1991)

              Isolated as a clone having weak homology to the 150kD subunit of yeast RNA polymerase II.

              (Kontermann et al., 1989)

              RpI135, encoding the second largest subunit of RNA polymerase II, has been cloned and sequenced.

              (Kontermann et al., 1989)
              Relationship to Other Genes
              Source for database merge of

              Source for merge of: RpI135 l(2)k16513

              (Campbell and Tomlinson, 1998)
              Additional comments
              Nomenclature History
              Source for database identify of

              Source for identity of: RpI135 CG4033

              (Guan, 1999.11)

              Source for identity of: Polr1B RpI135

              (Marygold et al., 2020)
              Nomenclature comments
              Etymology

              Named 'Polr1B' after the human ortholog.

              (Marygold et al., 2020)
              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 ( 48 )
              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/Swiss-Prot - Manually annotated and reviewed 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)
              Linkouts
              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
              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 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.
              References (76)