| 1998 |
Absence of RPA135 (the second-largest subunit of yeast RNA Pol I) triggers a gradual decrease in rDNA repeat number to ~half normal level, and reintroduction of RPA135 restores normal repeat number. This effect requires FOB1 (replication fork blocking protein), placing RNA Pol I/RPA135 as a regulator of rDNA copy number stability via replication fork blockage-stimulated recombination. |
Yeast genetic deletion/complementation (rpa135Δ mutants), rDNA copy number analysis, epistasis with fob1Δ |
Genes & development |
High |
9869636
|
| 1991 |
RPA135 was identified as one of at least nine genes (RRN1–RRN9) specifically required for RNA Pol I-dependent 35S rRNA synthesis in S. cerevisiae, established by a genetic screen using a GAL7-driven Pol II rescue system to identify mutants defective in Pol I transcription. |
Genetic screen for Pol I transcription mutants using GAL7-hybrid gene suppression system; red/white colony color assay and galactose-dependent growth test |
Proceedings of the National Academy of Sciences of the United States of America |
Medium |
1871118
|
| 1995 |
Yeast cells lacking RNA Pol I activity due to RPA135 gene disruption can survive by switching rDNA transcription to RNA Pol II via a cryptic Pol II promoter overlapping the Pol I promoter in rDNA. This demonstrates that RPA135 (and thus Pol I) is the sole normal source of 25S, 18S, and 5.8S rRNAs, and its loss is viable only through this polymerase switch. |
RPA135 gene disruption; RNA analysis of polymerase-specific transcripts; episomal rDNA characterization in petite mutants |
Molecular and cellular biology |
High |
7739526
|
| 2003 |
The C-terminal Zn-binding domain of Rpa135 (yeast POLR1B ortholog) is required for recruitment of the largest Pol I subunit Rpa190 into the RNA polymerase I complex. Nonfunctional Rpa135 mutants lacking this domain failed to assemble Pol I. Surprisingly, replacement of all four cysteines with alanines still yielded functional Rpa135, indicating the domain's essential role is structural rather than Zn2+-coordination per se. |
Mutagenesis of Zn-binding domain (individual and combinatorial cysteine-to-alanine substitutions); analysis of Pol I complex assembly |
Eukaryotic cell |
Medium |
14555487
|
| 2007 |
Specific point mutations in RPA135 (rpa135-L656P and rpa135-D395N) are lethal in combination with rpa34Δ or rpa49Δ mutations, placing RPA135 in a functional network with Rpa34 and Rpa49 subunits for Pol I transcription. The lobe domain of Rpa135 and the jaw domain of Rpa190 form a jaw-lobe interface critical for Pol I function. |
Yeast genetic epistasis; synthetic lethality analysis of double mutants; growth assays |
Molecular and cellular biology |
Medium |
18086878
|
| 2007 |
Mouse Rpo1-2 (POLR1B ortholog) is essential for pre-implantation development. A gene-trap truncation in exon 14 of Rpo1-2 (removing 312 aa from C-terminus) severely impairs rRNA synthesis, causes nucleolus disruption, and triggers apoptotic cell death by the morula stage in homozygous embryos. |
Gene trap insertional mutagenesis in mice; rRNA synthesis assay; histological analysis of embryos; nucleolar structure analysis |
Biochemical and biophysical research communications |
High |
18023416
|
| 2018 |
RPA135 (POLR1B) is required for BMH-21-mediated degradation of the largest Pol I subunit RPA194. Pol I preinitiation factors and polymerase subunits including RPA135 are necessary components of the conserved transcription elongation checkpoint activated by BMH-21, which directly impairs Pol I transcription elongation causing long-lived polymerase pausing. |
Genetic analyses in yeast and human cells; fully reconstituted Pol I transcription assay; small-molecule treatment (BMH-21); subunit dependency analysis |
Cell reports |
High |
29642000
|
| 2019 |
A super-active Pol I mutant allele RPA135-F301S restores normal rRNA synthesis and increases Pol I density on rDNA genes in the absence of Rpa49. The F301S mutation maps to the jaw-lobe interface of Pol I (lobe in Rpa135, jaw in Rpa190/Rpa12), and Pol I bearing this mutation is hyper-active in an in vitro tailed-template transcription assay, proposed to result from a conformational change supporting DNA insertion into the enzyme cleft. |
Genetic suppressor screen; rRNA synthesis assay; ChIP (Pol I density on rDNA); in vitro tailed-template transcription assay; structural mapping onto Pol I cryo-EM structure |
PLoS genetics |
High |
31136569
|
| 2019 |
Pathogenic variants in POLR1B cause Treacher Collins syndrome type 4 (TCS4). Knockdown of polr1b in zebrafish induces abnormal craniofacial phenotype mimicking TCS, associated with altered ribosomal gene expression, massive p53-dependent apoptosis in the neuroepithelium, and reduced number of neural crest cell (NCC) derivatives. |
Exome sequencing in human patients; zebrafish polr1b morpholino knockdown; craniofacial phenotyping; ribosomal gene expression analysis; apoptosis assay (p53-dependent); NCC derivative quantification |
Genetics in medicine : official journal of the American College of Medical Genetics |
High |
31649276
|
| 2020 |
RPA135 (POLR1B) silencing causes alterations in the expression and localization of Pol I subunits RPA194. Despite these alterations, the core Pol I complex between RPA194 and RPA135 remains intact upon RPA12 knockdown, and the transcription of Pol I and its engagement with chromatin remain unaffected when RPA12 is silenced. BMH-21-mediated degradation of RPA194 was found to be independent of RPA12. |
siRNA knockdown of RPA12; immunofluorescence (localization); co-immunoprecipitation (complex integrity); chromatin engagement assay; BMH-21 treatment |
PloS one |
Medium |
37167337
|
| 2023 |
Homozygous null mutations in Polr1b lead to preimplantation lethality in mice, and Polr1b-/- embryos exhibit defects in nucleolar structure (decreased nucleolar precursor bodies, increased nucleolar volume, single condensed nucleolus), demonstrating that POLR1B/Pol I function and rRNA transcription are required for maintaining nucleolar phase separation properties and integrity during development. |
Homozygous null mouse mutants (Polr1b-/-); live imaging and nucleolar structure analysis; pharmacological Pol I inhibition in embryos and hiPSCs; viscosity measurements of granular compartment |
PLoS genetics |
High |
37639467
|
| 2023 |
PAF49 (mammalian orthologue of yeast Rpa34) contains an 'arm' domain that directly interacts with POLR1B (PolR1B). This interaction is required for rDNA transcription; disrupting the PAF49–PolR1B interaction inhibits Pol I transcription in normal and cancer cells, arresting normal cells and killing cancer cells. |
Auxin-induced degron system for PAF49 degradation; domain deletion analysis; co-immunoprecipitation; rDNA transcription assay; cell growth/viability assays in normal and cancer cells |
The Journal of biological chemistry |
High |
37356716
|
| 2023 |
In vitro and in vivo analyses of the A34 family (PAF49/Rpa34) show that the 'arm' of A34 intimately interacts with PolR1B, PolR1A, and PolR1C subunits of Pol I as resolved by cryo-EM, placing this interaction at the structural interface of the Pol I complex. |
In silico structural analysis; cryo-EM structure interpretation; domain mapping |
Genes |
Low |
39858608
|
| 2026 |
TCS4-associated mutations R1022C and R1022S in Rpa2 (S. pombe POLR1B ortholog) cause Pol I to abnormally accumulate at the 5' region of rDNA, resulting in defective 35S pre-rRNA biogenesis, impaired cell growth under nutrient-rich conditions, and increased sensitivity to BMH-21. Rpa2 protein levels are unaffected, indicating the mutations impair Pol I elongation/progression rather than subunit stability. |
Introduction of TCS4-associated mutations in S. pombe rpa2; ChIP analysis of Pol I distribution on rDNA; pre-rRNA biogenesis analysis; growth assays; BMH-21 sensitivity assay |
FEBS open bio |
Medium |
41542823
|
| 2026 |
The SuperPol mutant RPA135-F301S produces 1.5-fold more rRNA than wild-type Pol I in yeast, linked to reduced premature termination of transcription (PTT). In vitro, SuperPol shows reduced nascent transcript cleavage and more efficient transcript elongation after pauses, at the cost of transcriptional fidelity. SuperPol is resistant to BMH-21 and maintains subunit stability under drug treatment, confirming that PTT is the mechanism by which BMH-21 inhibits wild-type Pol I. |
CRAC (cross-linking and analysis of cDNA); in vitro transcription assay; rRNA quantification; BMH-21 treatment; comparison of WT and RPA135-F301S mutant Pol I |
eLife |
High |
41677783
|
| 2014 |
A high-frequency interchromosomal interaction occurs between rDNA intergenic spacer (IGS1) and the intergenic region of the RPA135 locus in S. cerevisiae. A 75-bp sequence within the RPA135-tK(CUU)P intergenic region mediates this interaction, which is dependent on rDNA copy number and Msn2 protein. This interaction stabilizes rDNA repeat number and contributes to nucleolar stability, but does not govern RPA135 transcription. |
Quantitative chromosome conformation capture (qCCC); replacement mapping; rDNA copy number analysis; Msn2 deletion epistasis |
Molecular and cellular biology |
Medium |
25421713
|
| 2010 |
POLR1B was identified as a novel c-MYC target gene that is downregulated during granulocyte differentiation in concert with loss of c-MYC, and is reinduced in terminally differentiated granulocytes upon MYC-ER transgene activation. c-MYC coordinately regulates POLR1B and other Pol I factors alongside rDNA chromatin remodeling to control ribosomal RNA gene transcription. |
Gene expression arrays; MYC-ER transgene activation in differentiated granulocytes; Pol I loading on rDNA (ChIP); UBF depletion analysis |
Nucleic acids research |
Medium |
21177653
|