scholarly journals Nucleolar Components Involved in Ribosome Biogenesis Cycle between the Nucleolus and Nucleoplasm in Interphase Cells

2001 ◽  
Vol 153 (1) ◽  
pp. 169-176 ◽  
Author(s):  
Danyang Chen ◽  
Sui Huang
Keyword(s):  
Ribosome Biogenesis ◽  
Dynamic Properties ◽  
Ribosomal Subunit ◽  
Selective Inhibition ◽  
Rrna Synthesis ◽  
Functional Roles ◽  
Binding Factor ◽  
Upstream Binding Factor ◽  
Polymerase I ◽  
Nucleolar Components

We examined the mobilities of nucleolar components that act at various steps of the ribosome biogenesis pathway. Fluorescence recovery after photobleaching (FRAP) and fluorescence loss in photobleaching (FLIP) analyses demonstrate that factors involved in rRNA transcription (upstream-binding factor [UBF]), processing (nucleolin, fibrillarin, and RNase MRP subunits, Rpp29), and ribosome assembly (B23) exchange rapidly between the nucleoplasm and nucleolus. In contrast, the mobilities of ribosomal subunit proteins (S5, L9) are much slower. Selective inhibition of RNA polymerase I transcription does not prevent the exchanges but influences the rates of exchange differentially for different nucleolar components. These findings suggest that the rapid exchange of nucleolar components between the nucleolus and nucleoplasm may represent a new level of regulation for rRNA synthesis. The different dynamic properties of proteins involved in different steps of ribosome biogenesis imply that the nucleolar association of these proteins is due to their specific functional roles rather than simply their specific nucleolar-targeting events.

scholarly journals Modifications of both selectivity factor and upstream binding factor contribute to poliovirus-mediated inhibition of RNA polymerase I transcription

2005 ◽  
Vol 86 (8) ◽  
pp. 2315-2322 ◽  
Author(s):  
Rajeev Banerjee ◽  
Mary K. Weidman ◽  
Sonia Navarro ◽  
Lucio Comai ◽  
Asim Dasgupta
Keyword(s):  
Rna Polymerase ◽  
Rna Polymerase I ◽  
Rrna Synthesis ◽  
Selectivity Factor ◽  
Pol I ◽  
Binding Factor ◽  
Infected Cells ◽  
Upstream Binding Factor ◽  
Polymerase I

Soon after infection, poliovirus (PV) shuts off host-cell transcription, which is catalysed by all three cellular RNA polymerases. rRNA constitutes more than 50 % of all cellular RNA and is transcribed from rDNA by RNA polymerase I (pol I). Here, evidence has been provided suggesting that both pol I transcription factors, SL-1 (selectivity factor) and UBF (upstream binding factor), are modified and inactivated in PV-infected cells. The viral protease 3Cpro appeared to cleave the TATA-binding protein-associated factor 110 (TAF110), a subunit of the SL-1 complex, into four fragments in vitro. In vitro protease-cleavage assays using various mutants of TAF110 and purified 3Cpro indicated that the Q265G266 and Q805G806 sites were cleaved by 3Cpro. Both SL-1 and UBF were depleted in PV-infected cells and their disappearance correlated with pol I transcription inhibition. rRNA synthesis from a template containing a human pol I promoter demonstrated that both SL-1 and UBF were necessary to restore pol I transcription fully in PV-infected cell extracts. These results suggested that both SL-1 and UBF are transcriptionally inactivated in PV-infected HeLa cells.

scholarly journals LYAR potentiates rRNA synthesis by recruiting BRD2/4 and the MYST-type acetyltransferase KAT7 to rDNA

2019 ◽  
Vol 47 (19) ◽  
pp. 10357-10372 ◽  
Author(s):  
Keiichi Izumikawa ◽  
Hideaki Ishikawa ◽  
Harunori Yoshikawa ◽  
Sally Fujiyama ◽  
Akira Watanabe ◽  
...  
Keyword(s):  
Ribosomal Rna ◽  
Rna Polymerase I ◽  
Rrna Synthesis ◽  
Histone H4 ◽  
Rdna Transcription ◽  
Binding Factor ◽  
Rdna Loci ◽  
Upstream Binding Factor ◽  
Polymerase I ◽  
Cell Growth And Proliferation

Abstract Activation of ribosomal RNA (rRNA) synthesis is pivotal during cell growth and proliferation, but its aberrant upregulation may promote tumorigenesis. Here, we demonstrate that the candidate oncoprotein, LYAR, enhances ribosomal DNA (rDNA) transcription. Our data reveal that LYAR binds the histone-associated protein BRD2 without involvement of acetyl-lysine–binding bromodomains and recruits BRD2 to the rDNA promoter and transcribed regions via association with upstream binding factor. We show that BRD2 is required for the recruitment of the MYST-type acetyltransferase KAT7 to rDNA loci, resulting in enhanced local acetylation of histone H4. In addition, LYAR binds a complex of BRD4 and KAT7, which is then recruited to rDNA independently of the BRD2-KAT7 complex to accelerate the local acetylation of both H4 and H3. BRD2 also helps recruit BRD4 to rDNA. By contrast, LYAR has no effect on rDNA methylation or the binding of RNA polymerase I subunits to rDNA. These data suggest that LYAR promotes the association of the BRD2-KAT7 and BRD4-KAT7 complexes with transcription-competent rDNA loci but not to transcriptionally silent rDNA loci, thereby increasing rRNA synthesis by altering the local acetylation status of histone H3 and H4.

scholarly journals UBF levels determine the number of active ribosomal RNA genes in mammals

2008 ◽  
Vol 183 (7) ◽  
pp. 1259-1274 ◽  
Author(s):  
Elaine Sanij ◽  
Gretchen Poortinga ◽  
Kerith Sharkey ◽  
Sandy Hung ◽  
Timothy P. Holloway ◽  
...  
Keyword(s):  
Ribosomal Rna ◽  
High Mobility ◽  
Rrna Genes ◽  
Rrna Synthesis ◽  
Rrna Gene ◽  
Extracellular Signal ◽  
Binding Factor ◽  
Upstream Binding Factor ◽  
Polymerase I

In mammals, the mechanisms regulating the number of active copies of the ∼200 ribosomal RNA (rRNA) genes transcribed by RNA polymerase I are unclear. We demonstrate that depletion of the transcription factor upstream binding factor (UBF) leads to the stable and reversible methylation-independent silencing of rRNA genes by promoting histone H1–induced assembly of transcriptionally inactive chromatin. Chromatin remodeling is abrogated by the mutation of an extracellular signal-regulated kinase site within the high mobility group box 1 domain of UBF1, which is required for its ability to bend and loop DNA in vitro. Surprisingly, rRNA gene silencing does not reduce net rRNA synthesis as transcription from remaining active genes is increased. We also show that the active rRNA gene pool is not static but decreases during differentiation, correlating with diminished UBF expression. Thus, UBF1 levels regulate active rRNA gene chromatin during growth and differentiation.

A role for upstream binding factor in organizing ribosomal gene chromatin

2006 ◽  
Vol 73 ◽  
pp. 77-84 ◽  
Author(s):  
Jane E. Wright ◽  
Christine Mais ◽  
José-Luis Prieto ◽  
Brian McStay
Keyword(s):  
Nucleolar Organizer ◽  
Ribosomal Gene ◽  
Rna Polymerase I ◽  
Nucleolar Organizer Regions ◽  
Binding Factor ◽  
Upstream Binding Factor ◽  
Acrocentric Chromosomes ◽  
Polymerase I ◽  
Secondary Constrictions ◽  
Active Nors

Human ribosomal genes are located in NORs (nucleolar organizer regions) on the short arms of acrocentric chromosomes. During metaphase, previously active NORs appear as prominent chromosomal features termed secondary constrictions, which are achromatic in chromosome banding and positive in silver staining. The architectural RNA polymerase I transcription factor UBF (upstream binding factor) binds extensively across the ribosomal gene repeat throughout the cell cycle. Evidence that UBF underpins NOR structure is provided by an examination of cell lines in which large arrays of a heterologous UBF binding sequences are integrated 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, that are morphologically similar to NORs.

scholarly journals Epigenetic Programming of the rRNA Promoter by MBD3

2007 ◽  
Vol 27 (13) ◽  
pp. 4938-4952 ◽  
Author(s):  
Shelley E. Brown ◽  
Moshe Szyf
Keyword(s):  
Small Interfering Rna ◽  
Rna Polymerase I ◽  
Rrna Genes ◽  
Rrna Gene ◽  
Rrna Transcription ◽  
Epigenetic Programming ◽  
Binding Factor ◽  
Upstream Binding Factor ◽  
Polymerase I ◽  
Interfering Rna

ABSTRACT Within the human genome there are hundreds of copies of the rRNA gene, but only a fraction of these genes are active. Silencing through epigenetics has been extensively studied; however, it is essential to understand how active rRNA genes are maintained. Here, we propose a role for the methyl-CpG binding domain protein MBD3 in epigenetically maintaining active rRNA promoters. We show that MBD3 is localized to the nucleolus, colocalizes with upstream binding factor, and binds to unmethylated rRNA promoters. Knockdown of MBD3 by small interfering RNA results in increased methylation of the rRNA promoter coupled with a decrease in RNA polymerase I binding and pre-rRNA transcription. Conversely, overexpression of MBD3 results in decreased methylation of the rRNA promoter. Additionally, overexpression of MBD3 induces demethylation of nonreplicating plasmids containing the rRNA promoter. We demonstrate that this demethylation occurs following the overexpression of MBD3 and its increased interaction with the methylated rRNA promoter. This is the first demonstration that MBD3 is involved in inducing and maintaining the demethylated state of a specific promoter.

scholarly journals Recruitment of TATA-Binding Protein–TAFI Complex SL1 to the Human Ribosomal DNA Promoter Is Mediated by the Carboxy-Terminal Activation Domain of Upstream Binding Factor (UBF) and Is Regulated by UBF Phosphorylation

1999 ◽  
Vol 19 (4) ◽  
pp. 2872-2879 ◽  
Author(s):  
JoAnn C. Tuan ◽  
Weiguo Zhai ◽  
Lucio Comai
Keyword(s):  
Dna Binding ◽  
Ribosomal Dna ◽  
Transcriptional Activation ◽  
Direct Contact ◽  
Binding Protein ◽  
Tata Binding Protein ◽  
Rrna Synthesis ◽  
Binding Factor ◽  
Upstream Binding Factor ◽  
Carboxy Terminal

ABSTRACT Human rRNA synthesis by RNA polymerase I requires at least two auxiliary factors, upstream binding factor (UBF) and SL1. UBF is a DNA binding protein with multiple HMG domains that binds directly to the CORE and UCE elements of the ribosomal DNA promoter. The carboxy-terminal region of UBF is necessary for transcription activation and has been shown to be extensively phosphorylated. SL1, which consists of TATA-binding protein (TBP) and three associated factors (TAFIs), does not have any sequence-specific DNA binding activity, and its recruitment to the promoter is mediated by specific protein interactions with UBF. Once on the promoter, the SL1 complex makes direct contact with the DNA promoter and directs promoter-specific initiation of transcription. To investigate the mechanism of UBF-dependent transcriptional activation, we first performed protein-protein interaction assays between SL1 and a series of UBF deletion mutants. This analysis indicated that the carboxy-terminal domain of UBF, which is necessary for transcriptional activation, makes direct contact with the TBP-TAFI complex SL1. Since this region of UBF can be phosphorylated, we then tested whether this modification plays a functional role in the interaction with SL1. Alkaline phosphatase treatment of UBF completely abolished the ability of UBF to interact with SL1; moreover, incubation of the dephosphorylated UBF with nuclear extracts from exponentially growing cells was able to restore the UBF-SL1 interaction. In addition, DNase I footprinting analysis and in vitro-reconstituted transcription assays with phosphatase-treated UBF provided further evidence that UBF phosphorylation plays a critical role in the regulation of the recruitment of SL1 to the ribosomal DNA promoter and stimulation of UBF-dependent transcription.

scholarly journals Upstream binding factor stabilizes Rib 1, the TATA-binding-protein-containing Xenopus laevis RNA polymerase I transcription factor, by multiple protein interactions in a DNA-independent manner.

1996 ◽  
Vol 16 (10) ◽  
pp. 5572-5578 ◽  
Author(s):  
M Bodeker ◽  
C Cairns ◽  
B McStay
Keyword(s):  
Xenopus Laevis ◽  
Rna Polymerase ◽  
Protein Interactions ◽  
Tata Binding Protein ◽  
Rna Polymerase I ◽  
Independent Manner ◽  
Multiple Protein ◽  
Binding Factor ◽  
Upstream Binding Factor ◽  
Polymerase I

Initiation of RNA polymerase I transcription in Xenopus laevis requires Rib 1 and upstream binding factor (UBF). UBF and Rib 1 combine to form a stable transcription complex on the Xenopus ribosomal gene promoter. Here we show that Rib 1 comprises TATA-binding protein (TBP) and TBP-associated factor components. Thus, Rib 1 is the Xenopus equivalent of mammalian SL 1. In contrast to SL 1, Rib 1 is an unstable complex that readily dissociates into TBP and associated components. We identify a novel function for UBF in stabilizing Rib 1 by multiple protein interactions. This stabilization occurs in solution in a DNA-independent manner. These results may partially explain the difference in UBF requirement between Xenopus and mammalian systems.

scholarly journals TBP-TAF Complex SL1 Directs RNA Polymerase I Pre-initiation Complex Formation and Stabilizes Upstream Binding Factor at the rDNA Promoter

2005 ◽  
Vol 280 (33) ◽  
pp. 29551-29558 ◽  
Author(s):  
J. Karsten Friedrich ◽  
Kostya I. Panov ◽  
Pavel Cabart ◽  
Jackie Russell ◽  
Joost C. B. M. Zomerdijk
Keyword(s):  
Complex Formation ◽  
Rna Polymerase ◽  
Rna Polymerase I ◽  
Initiation Complex ◽  
Binding Factor ◽  
Upstream Binding Factor ◽  
Polymerase I
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