Affinage

POLR3GL

DNA-directed RNA polymerase III subunit RPC7-like · UniProt Q9BT43

Length
218 aa
Mass
25.3 kDa
Annotated
2026-04-28
17 papers in source corpus 8 papers cited in narrative 8 extracted findings

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

POLR3GL encodes RPC7β, a subunit of RNA polymerase III that is incorporated mutually exclusively with its paralog POLR3G (RPC7α), generating two distinct Pol III isoforms (Pol IIIα and Pol IIIβ) that arose from a vertebrate-specific gene duplication (PMID:24107381, PMID:36710885). Both isoforms occupy the same genomic target genes and can partially compensate for each other in vivo, yet they differ in transcriptional output at specific loci such as snaR-A and in upstream regulation, as MYC controls POLR3G but not POLR3GL (PMID:24107381, PMID:35637192). POLR3GL is ubiquitously expressed and upregulated during differentiation, whereas POLR3G is enriched in stem and cancer cells; accordingly, POLR3GL knockout mice complete embryogenesis but die postnatally with growth and cerebellar defects (PMID:30820548, PMID:32576691, PMID:31173763). Biallelic loss-of-function variants in POLR3GL cause human developmental syndromes featuring endosteal hyperostosis, oligodontia, short stature, and neonatal progeroid features (PMID:31089205, PMID:31695177).

Mechanistic history

Synthesis pass · year-by-year structured walk · 5 steps
  1. 2013 High

    Establishing that POLR3GL and POLR3G arose by DNA-based gene duplication and encode interchangeable Pol III subunits that occupy the same target genes resolved the question of whether two RPC7 paralogs have divergent or redundant target specificity, revealing that neofunctionalization occurred at the level of transcriptional regulation (MYC binding) rather than target gene selection.

    Evidence ChIP-seq occupancy profiling, promoter-binding assays, and phylogenomic analysis in multiple human cell lines

    PMID:24107381

    Open questions at the time
    • Whether any loci show quantitative differences in transcription between the two isoforms was not resolved
    • Mechanism by which MYC regulation of POLR3G but not POLR3GL impacts Pol III output was unexplored
    • In vivo consequences of losing either isoform were unknown
  2. 2019 High

    Demonstrating that POLR3G depletion but not POLR3GL depletion triggers proliferative arrest and differentiation in cancer cells, and that the two isoforms differ in expression across differentiation states, established that the paralogs have functionally distinct roles in cell fate control despite shared target occupancy.

    Evidence siRNA knockdown with proliferation/differentiation assays in prostate cancer cells [PMID:30820548]; tRNA microarray and expression analysis during Xenopus muscle differentiation [PMID:31173763]

    PMID:30820548 PMID:31173763

    Open questions at the time
    • Which specific Pol III transcript changes mediate the differentiation phenotype was not identified
    • Whether the isoform switch during differentiation is cause or consequence of lineage commitment was unresolved
  3. 2019 Medium

    Identification of biallelic loss-of-function variants in POLR3GL in patients with skeletal dysplasia/oligodontia and neonatal progeroid syndrome established POLR3GL as essential for human skeletal and dental development and demonstrated that POLR3G cannot fully compensate for POLR3GL loss in these tissues.

    Evidence Whole-exome sequencing with RNA-seq confirmation of nonsense-mediated decay/aberrant splicing in patient samples

    PMID:31089205 PMID:31695177

    Open questions at the time
    • No in vitro functional reconstitution or cellular rescue experiments were performed
    • Which Pol III transcripts are specifically disrupted in affected tissues is unknown
    • Single-family studies without independent replication for each variant
  4. 2020 High

    Knockout mouse studies resolved the in vivo essentiality question: POLR3GL is dispensable for embryogenesis but required for postnatal survival, and exogenous POLR3GL rescues POLR3G-knockout ES cell differentiation defects, proving partial functional interchangeability of the two isoforms.

    Evidence POLR3GL knockout mice, ES cell differentiation rescue, in vitro transcription, and ChIP-seq

    PMID:32576691

    Open questions at the time
    • Precise cause of postnatal lethality (cerebellar vs. systemic growth failure) was not definitively resolved
    • Whether double knockout is embryonic lethal was not tested
    • Tissue-specific requirements for each isoform remain unmapped
  5. 2022 High

    Demonstrating that POLR3G loss restricts the Pol III transcriptional repertoire at specific loci (notably snaR-A) while POLR3GL-containing Pol III cannot maintain equivalent output resolved how two isoforms sharing target genes produce distinct transcriptional outcomes.

    Evidence POLR3G knockout with ChIP-seq, RNA-seq, and chromatin feature analysis

    PMID:35637192

    Open questions at the time
    • Structural basis for why snaR-A and other loci are preferentially sensitive to isoform identity is unknown
    • Whether POLR3GL-containing Pol III has its own uniquely dependent loci has not been tested
    • Downstream functional consequences of snaR-A loss are unclear

Open questions

Synthesis pass · forward-looking unresolved questions
  • The structural determinants within RPC7β versus RPC7α that confer locus-specific transcriptional differences, the full set of Pol III targets uniquely dependent on each isoform, and the tissue-specific mechanisms underlying the human disease phenotypes of POLR3GL deficiency remain unresolved.
  • No high-resolution structure of Pol IIIβ (POLR3GL-containing) complex has been solved
  • Tissue-specific Pol III transcript profiling in POLR3GL-deficient contexts is lacking
  • Genotype-phenotype correlation across different POLR3GL variants is incomplete

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0005198 structural molecule activity 3
Localization
GO:0005634 nucleus 3
Pathway
R-HSA-74160 Gene expression (Transcription) 4
Partners
POLR3G
Complex memberships
RNA polymerase III

Evidence

Reading pass · 8 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2013 POLR3GL and POLR3G arose from a DNA-based gene duplication in a common ancestor of vertebrates, resulting in two distinct Pol III isoforms. Both POLR3GL- and POLR3G-containing Pol III occupy the same target genes in very constant proportions within a cell line, indicating similar target gene specificity. However, unlike POLR3G, the POLR3GL promoter does not bind the transcription factor MYC, demonstrating neofunctionalization at the level of transcriptional regulation rather than protein function. ChIP-seq genome-wide occupancy profiling, promoter-binding assays, phylogenetic/genomic analysis of gene duplication Genome research High 24107381
2019 POLR3GL is ubiquitously expressed whereas POLR3G is enriched in undifferentiated/cancer cells. Selective depletion of POLR3GL does not trigger proliferative arrest or differentiation of prostate cancer cells, in contrast to POLR3G depletion, establishing that the two Pol III isoforms have functionally distinct roles in controlling cell fate despite occupying the same target genes. siRNA-mediated knockdown of POLR3GL vs. POLR3G with proliferation and differentiation assays in prostate cancer cell lines Nucleic acids research High 30820548
2020 POLR3GL-containing Pol III (Pol IIIβ) and POLR3G-containing Pol III (Pol IIIα) bind the same target genes and perform the same transcriptional functions both in vitro and in vivo, and can compensate for each other to a significant degree. POLR3GL knockout mice complete embryonic development but die ~3 weeks after birth with growth defects and potential cerebellar neuronal defects, demonstrating that POLR3GL is essential for postnatal viability. Exogenous POLR3GL expression rescues the differentiation defect of POLR3G knockout embryonic stem cells. Knockout mouse generation, embryonic stem cell differentiation assays, in vitro transcription assays, ChIP-seq Proceedings of the National Academy of Sciences of the United States of America High 32576691
2022 Loss of POLR3G (RPC7α) but not POLR3GL (RPC7β) leads to a restricted repertoire of Pol III-transcribed genes, with snaR-A noncoding RNA being particularly sensitive to POLR3G loss. POLR3GL-containing Pol III cannot maintain snaR-A transcription at levels equivalent to POLR3G-containing Pol III, indicating that the two isoforms have distinct transcriptional outputs at specific loci despite shared target occupancy. POLR3G knockout, ChIP-seq, RNA-seq, analysis of chromatin features at Pol III target genes Nature communications High 35637192
2019 During skeletal muscle differentiation in Xenopus, Polr3gL (the ortholog of POLR3GL) is upregulated alongside contractile protein genes, while Polr3g is expressed early in the myogenic lineage. The two isoforms have distinct activities on tRNA isoacceptor synthesis as shown by custom tRNA microarray. Forcing Polr3g expression during differentiation partially reverses myogenic differentiation, while Pol III-dependent transcripts are dramatically downregulated during muscle differentiation. tRNA microarray, expression analysis during Xenopus embryonic development, Polr3g overexpression in differentiating muscle cells Developmental biology Medium 31173763
2019 Biallelic loss-of-function splice acceptor site variants in POLR3GL cause loss of full-length POLR3GL RNA transcripts (confirmed by RNA sequencing), resulting in a clinical syndrome of axial endosteal hyperostosis, oligodontia, short stature, and mild facial dysmorphisms, establishing POLR3GL as an essential Pol III subunit in human skeletal and dental development. Whole exome sequencing, RNA sequencing to confirm nonsense-mediated decay/aberrant splicing of POLR3GL transcripts in patient blood European journal of human genetics : EJHG Medium 31089205
2019 A homozygous nonsense variant in POLR3GL (p.Arg120Ter) leads to nonsense-mediated decay of POLR3GL transcripts (confirmed by RNA studies), causing a variant of neonatal progeroid syndrome, further establishing the essential in vivo role of POLR3GL as a subunit of RNA polymerase III in human development. Exome sequencing, RNA expression studies demonstrating nonsense-mediated decay European journal of human genetics : EJHG Medium 31695177
2023 Structural and genomic studies reveal that POLR3GL (RPC7β) and POLR3G (RPC7α) have distinct protein characteristics, and that Pol III identity (determined by which RPC7 subunit is incorporated) underlies differential Pol III transcription patterns. The two subunits are mutually exclusively incorporated into the Pol III complex. Review integrating structural data and genomic studies; mutually exclusive subunit incorporation established by prior biochemical fractionation and ChIP-seq Frontiers in molecular biosciences Medium 36710885

Source papers

Stage 0 corpus · 17 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2021 RNA Polymerase III Subunit Mutations in Genetic Diseases. Frontiers in molecular biosciences 53 34395528
2013 Gene duplication and neofunctionalization: POLR3G and POLR3GL. Genome research 46 24107381
2019 Effects on prostate cancer cells of targeting RNA polymerase III. Nucleic acids research 38 30820548
2021 The nuclear and cytoplasmic activities of RNA polymerase III, and an evolving transcriptome for surveillance. Nucleic acids research 33 34850129
2019 Biallelic variants in POLR3GL cause endosteal hyperostosis and oligodontia. European journal of human genetics : EJHG 30 31089205
2022 A cancer-associated RNA polymerase III identity drives robust transcription and expression of snaR-A noncoding RNA. Nature communications 27 35637192
2020 Functions of paralogous RNA polymerase III subunits POLR3G and POLR3GL in mouse development. Proceedings of the National Academy of Sciences of the United States of America 26 32576691
2019 A variant of neonatal progeroid syndrome, or Wiedemann-Rautenstrauch syndrome, is associated with a nonsense variant in POLR3GL. European journal of human genetics : EJHG 23 31695177
2022 The POLR3G Subunit of Human RNA Polymerase III Regulates Tumorigenesis and Metastasis in Triple-Negative Breast Cancer. Cancers 15 36497214
2021 Identification of Novel Metabolism-Associated Subtypes for Pancreatic Cancer to Establish an Eighteen-Gene Risk Prediction Model. Frontiers in cell and developmental biology 15 34447748
2023 Significance of liquid-liquid phase separation (LLPS)-related genes in breast cancer: a multi-omics analysis. Aging 13 37338518
2019 Skeletal muscle differentiation drives a dramatic downregulation of RNA polymerase III activity and differential expression of Polr3g isoforms. Developmental biology 10 31173763
2023 RNA polymerase III transcription and cancer: A tale of two RPC7 subunits. Frontiers in molecular biosciences 6 36710885
2023 A Combinatorial Regulatory Platform Determines Expression of RNA Polymerase III Subunit RPC7α (POLR3G) in Cancer. Cancers 4 37894362
2025 Comprehensive genotype-phenotype analysis in POLR3-related disorders. HGG advances 2 40684265
2025 Optimized network inference for immune diseased single cells. Frontiers in immunology 0 40777011
2023 [Wiedemann-Rautenstrauch syndrome. The first description of a clinical case in the Russian Federation]. Problemy endokrinologii 0 38796765