Identification of two forms of the RNA polymerase I transcription factor UBF.

O’Mahony, Donagh; Rothblum, Lawrence I.

doi:10.1073/pnas.88.8.3180

Cited by 113 publications

(70 citation statements)

References 33 publications

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“…The UBF gene is differentially spliced, giving rise to two protein isoforms referred to as UBF1 and UBF2, the form with HMG box 2 deleted (Fig. 4, top) (8,33,44,53). The UBF1 transcription factor activates rRNA genes, whereas UBF2 is essentially inactive.…”

Section: Resultsmentioning

confidence: 99%

“…UBF function is regulated by phosphorylation in a cell cycledependent manner, and UBF phosphorylation plays a role in modulating recruitment of SL1 to the rRNA promoter, which influences its transcriptional activity (31,53,72,77,79,80,81). The kinases that phosphorylate UBF during cell cycle progression include cyclin (D1, A, and E)-dependent kinases (79,80), and these could enhance the ability of UBF to potentiate ␤-catenin-LEF/TCF signaling.…”

Section: Discussionmentioning

confidence: 99%

“…After several rounds of enrichment for active cDNA clones, the HMG box transcription factor, UBF2, was isolated. Mammalian cells contain two UBF isoforms with molecular masses of 97 and 94 kDa, which are generated by alternative splicing of a common RNA precursor (8,33,53). The 97-kDa efficiency of the luciferase reporter gene, 10 ng of pRL-TK Renilla luciferase expression vector (Promega) was cotransfected with each sample.…”

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A Functional Screen in Human Cells Identifies UBF2 as an RNA Polymerase II Transcription Factor That Enhances the β-Catenin Signaling Pathway

Grueneberg

Pablo

et al. 2003

Molecular and Cellular Biology

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␤-Catenin signaling plays an important role in the development of many organisms and has a key part in driving the malignant transformation of epithelial cells comprising a variety of cancers. ␤-Catenin can activate gene expression through its association with transcription factors of the lymphoid enhancer factor 1 (LEF-1)/T-cell factor (TCF) family. We designed a screen in human cells to identify novel genes that activate a ␤-catenin-LEF/TCF-responsive promoter and isolated the high-mobility group box transcription factor, UBF2. UBF1 and UBF2 are splice variants of a common precursor RNA. Although UBF1 has been shown to activate RNA polymerase I-regulated genes, the function of UBF2 has remained obscure. Here, we show for the first time that both UBF1 and UBF2 activate RNA polymerase II-regulated promoters. UBF2 associates with LEF-1, as shown by coimmunoprecipitation experiments, and potentiates transcriptional activation stimulated by LEF-1/␤-catenin from a synthetic promoter with multimerized LEF/TCF binding sites and a natural cyclin D1 promoter with consensus LEF/TCF binding sites. Downregulation of endogenous UBF expression using an RNA interference approach reduces transcriptional activation of a ␤-catenin-LEF/TCF-responsive promoter by means of overexpressed ␤-catenin, further implicating UBF as a transcriptional enhancer of the ␤-catenin pathway.

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Section: Resultsmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

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confidence: 99%

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A Functional Screen in Human Cells Identifies UBF2 as an RNA Polymerase II Transcription Factor That Enhances the β-Catenin Signaling Pathway

Grueneberg

Pablo

et al. 2003

Molecular and Cellular Biology

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“…UBF 2 differs from UBF 1 in missing 37 residues from the second HMG box (O'Mahony and Rothblum 1991). This deletion renders UBF 2 nonfunctional at the promoter (Kuhn et al 1994).…”

Section: Ubf Binds To Xen Arrays In Vivomentioning

confidence: 99%

UBF-binding site arrays form pseudo-NORs and sequester the RNA polymerase I transcription machinery

Mais¹,

Wright²,

Prieto³

et al. 2004

Genes Dev.

163

191

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Human ribosomal genes (rDNA) are located in nucleolar organizer regions (NORs) on the short arms of acrocentric chromosomes. Metaphase NORs that were transcriptionally active in the previous cell cycle appear as prominent chromosomal features termed secondary constrictions that are achromatic in chromosome banding and positive in silver staining. The architectural RNA polymerase I (pol I) transcription factor UBF binds extensively across rDNA throughout the cell cycle. To determine if UBF binding underpins NOR structure, we integrated large arrays of heterologous UBF-binding sequences at ectopic sites on human chromosomes. These arrays efficiently recruit UBF even to sites outside the nucleolus and, during metaphase, form novel silver stainable secondary constrictions, termed pseudo-NORs, morphologically similar to NORs. We demonstrate for the first time that in addition to UBF the other components of the pol I machinery are found associated with sequences across the entire human rDNA repeat. Remarkably, a significant fraction of these same pol I factors are sequestered by pseudo-NORs independent of both transcription and nucleoli. Because of the heterologous nature of the sequence employed, we infer that sequestration is mediated primarily by protein-protein interactions with UBF. These results suggest that extensive binding of UBF is responsible for formation and maintenance of the secondary constriction at active NORs. Furthermore, we propose that UBF mediates recruitment of the pol I machinery to nucleoli independently of promoter elements.[Keywords: RNA polymerase I; ribosomal DNA; nucleolar organiser region; nucleolus; upstream-binding factor] Supplemental material is available at http://www.genesdev.org.

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“…It contains five high mobility group boxes, an N terminus necessary for nuclear translocation, and a highly acidic C terminus essential for nucleolar localization (4,6,7). Although UBF is involved in pol I transcriptional activation, the mechanism by which it acts remains unclear.…”

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Upstream binding factor association induces large-scale chromatin decondensation

Chen

Belmont

Huang

2004

Proc. Natl. Acad. Sci. U.S.A.

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The function of upstream binding factor (UBF), an essential component of the RNA polymerase (pol) I preinitiation complex, is unclear. Recently, UBF was found distributed throughout ribosomal gene repeats rather than being restricted to promoter regions. This observation has led to the speculation that one role of UBF binding may be to induce chromatin remodeling. To directly evaluate the impact of UBF on chromatin structure, we used an in vivo assay in which UBF is targeted via a lac repressor fusion protein to a heterochromatic, amplified chromosome region containing lac operator repeats. We show that the association of UBF with this locus induces large-scale chromatin decondensation. This process does not appear to involve common remodeling complexes, including SWI͞SNF and histone acetyltransferases, and is independent of histone H3 lysine 9 acetylation. However, UBF recruits the pol I-specific, TATA box-binding protein containing complex SL1 and pol I subunits. Our results suggest a working hypothesis in which the dynamic association of UBF with ribosomal DNA clusters recruits the pol I transcription machinery and maintains these loci in a transcriptionally competent configuration. These studies also provide an in vivo model simulating ribosomal DNA transactivation outside the nucleolus, allowing temporal and spatial analyses of chromatin remodeling and assembly of the pol I transcription machinery. R ibosomal RNA (rRNA) is encoded by tandem arrays of rDNA genes that are organized in human cells into nucleolar organizing regions (NORs) located on five chromosome pairs. A specific set of transcription factors is dedicated to transcription of rDNA into pre-rRNA that is subsequently processed into 28S, 18S, and 5.8S rRNAs. The rRNAs are packaged with ribosomal proteins to form the large and small subunits of ribosomes (1). Transcription of rDNA is highly specific and extensively regulated, involving a large number of proteins (1-3). Studies based mostly on in vitro assays suggest that transcriptional activation of rDNA involves association of the preinitiation complex with the promoter region followed by recruitment of other factors and RNA polymerase (pol) I subunits. The preinitiation complex has been shown to contain upstream binding factor (UBF) (4) and the TATA box-binding protein (TBP) containing complex SL1 (5).UBF is highly conserved in vertebrate cells from Xenopus to human. It contains five high mobility group boxes, an N terminus necessary for nuclear translocation, and a highly acidic C terminus essential for nucleolar localization (4, 6, 7). Although UBF is involved in pol I transcriptional activation, the mechanism by which it acts remains unclear. The consensus derived mostly from in vitro and some in vivo correlative studies places UBF at the early steps of rDNA transactivation (1, 2, 8). Analyses using in vitro transcription assays indicate that UBF initially binds DNA and is necessary for SL1 binding to form the preinitiation complex (9). Recently, UBF was discovered to literally coat DNA thro...

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Identification of two forms of the RNA polymerase I transcription factor UBF.

Cited by 113 publications

References 33 publications

A Functional Screen in Human Cells Identifies UBF2 as an RNA Polymerase II Transcription Factor That Enhances the β-Catenin Signaling Pathway

A Functional Screen in Human Cells Identifies UBF2 as an RNA Polymerase II Transcription Factor That Enhances the β-Catenin Signaling Pathway

UBF-binding site arrays form pseudo-NORs and sequester the RNA polymerase I transcription machinery

Upstream binding factor association induces large-scale chromatin decondensation

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