Virtually the Entire Xenopus laevis rDNA Multikilobase Intergenic Spacer Serves to Stimulate Polymerase I Transcription

Mougey, Edward B.; Pape, Louise; Sollner‐Webb, Barbara

doi:10.1074/jbc.271.43.27138

Cited by 26 publications

(34 citation statements)

References 58 publications

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“…A role for region 0 and/or region 1 repeats in transcriptional enhancement is made controversial by our results, which do not fully support those of Mougey et al (26). These authors found that region 0 repeats could act as enhancers whose strength was proportional to the repeat copy number.…”

Section: Discussioncontrasting

confidence: 99%

“…3) did regions 0/1 show enhancer function, and even in these experiments, the region 0/1 repeats did not confer on an adjacent promoter the ability to withstand competition from a promoter bearing 60/81-bp enhancers. One possible explanation could be that Mougey et al (26) used X. borealis oocytes exclusively, whereas most of our studies were done using X. laevis oocytes. However, the fact that in our hands regions 0 and 1 also failed to reveal enhancer function in X. borealis oocytes (Fig.…”

Section: Discussionmentioning

confidence: 93%

“…A fragment containing both region 0 and region 1 has been reported to possess strong enhancer activity in X. borealis oocytes (26). Using X. laevis oocytes, we conducted similar tests of regions 0 and 1 in competition with enhancer-less and enhancer-bearing minigenes.…”

Section: Resultsmentioning

confidence: 99%

“…A study using X. laevis minigenes microinjected into X. borealis oocytes led to the conclusion that regions 0/1 are strong enhancers of transcription, perhaps even stronger than 60/81-bp repeats (26). These data combined with prior studies of 60/81-bp repeats and spacer promoters have collectively suggested that essentially all of the intergenic spacer serves to stimulate transcription from the downstream gene promoter.…”

mentioning

confidence: 96%

“…However, a role for spacer promoters and/or regions 0 and 1 has never been ruled out. The report that regions 0 and 1 possess strong enhancer activity (26) in oocytes has underscored the need to re-investigate the sequences responsible for nucleolar dominance-like rRNA gene competition.…”

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confidence: 99%

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Xenopus Ribosomal RNA Gene Intergenic Spacer Elements Conferring Transcriptional Enhancement and Nucleolar Dominance-like Competition in Oocytes

Caudy¹,

Pikaard

2002

Journal of Biological Chemistry

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Repeated within the intergenic spacers that separate adjacent ribosomal RNA (rRNA) genes in Xenopus laevis are several distinct sequence elements. These include transcription terminators, "region 0" repeats, "region 1" repeats, duplicated spacer promoters, and 42-bp enhancer elements that are embedded within 60 or 81-bp repeats. All have been reported to stimulate RNA polymerase I transcription from an adjacent gene promoter. A greater number of 42-bp enhancers/gene have been suggested to explain the preferential transcription of X. laevis rRNA genes in X. laevis x Xenopus borealis hybrids, an epigenetic phenomenon known as nucleolar dominance. However, the possible contribution of regions 0/1 and/or spacer promoters to the preferential transcription of X. laevis (over X. borealis) rRNA genes has never been tested directly. In this study, we systematically tested the various intergenic spacer elements for their contributions to promoter strength and nucleolar dominance-like competition in oocytes. In disagreement with a previous report, region 0 and region 1 repeats do not have significant enhancer activity, nor do they play a discernible role in X. laevis-X. borealis rRNA gene competition. Minigenes containing X. laevis spacer sequences are only dominant over minigenes having complete X. borealis spacers if a spacer promoter is located upstream of the 42-bp enhancers; X. laevis enhancers alone are not sufficient. These results provide additional evidence that spacer promoters together with adjacent enhancers form a functional activating unit in Xenopus oocytes.In Xenopus as in other eukaryotes, RNA polymerase I is dedicated to the transcription of ribosomal RNA genes, producing a 40 S primary transcript that is then processed into the 18 S, 5.8 S, and 28 S RNAs found within cytoplasmic ribosomes (1-5). There are hundreds (sometimes thousands) of rRNA genes in eukaryotic genomes. These rRNA genes are tandemly arrayed in head-to-tail clusters that are known as nucleolus organizer regions because nucleoli, the sites of ribosome assembly, are formed at the loci where rRNA genes are actively transcribed (6 -9).Within the nucleolus organizer regions, adjacent rRNA genes are separated by an intergenic spacer that typically contains repetitive DNA sequences, some of which have defined roles in transcriptional regulation (10). Intergenic spacers of Xenopus laevis have been particularly well characterized (Fig. 1). In oocytes injected with plasmid minigenes, the 60-and 81-bp repeats located just upstream of the X. laevis rRNA gene promoter act as orientation-and distance-independent enhancers of transcription (11). These elements are very similar, 81-bp repeats being 60-bp enhancers with an additional 21-bp extension (12, 13). Within each 60/81-bp enhancer is a 42-bp sequence that is ϳ80% identical to an upstream domain of the gene promoter (nucleotides Ϫ114 to Ϫ72 relative to the transcription start site, ϩ1). A synthetic oligonucleotide corresponding to this upstream promoter region is sufficient for strong orientatio...

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Section: Discussioncontrasting

confidence: 99%

Section: Discussionmentioning

confidence: 93%

Section: Resultsmentioning

confidence: 99%

mentioning

confidence: 96%

mentioning

confidence: 99%

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Xenopus Ribosomal RNA Gene Intergenic Spacer Elements Conferring Transcriptional Enhancement and Nucleolar Dominance-like Competition in Oocytes

Caudy¹,

Pikaard

2002

Journal of Biological Chemistry

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Molecular Cell Biology: Organization and Molecular Evolution of rDNA, Nucleolar Dominance, and Nucleolus Structure

et al. 2004

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Recently, the ribosomes -molecularly well-characterized cell organelles where the process of translation of messenger RNA into polypeptides occurs -have attracted new interest since they can be considered as a huge ribozyme-like complex consisting of different proteins and RNA -the RNAs mainly fulfilling functional tasks in translation, the proteins serving more structural functions (Moore and Steitz 2002). Within the eukaryotic cell, two (animals and fungi) or three (plants) sites of a translational machinery are present, the cytoplasm, mitochondria and chloroplasts, and, respectively, the components are mostly encoded in the cell nucleus or the mitochondrial or chloroplast genome. Since new insights are gained into the production and the assembly of the ribosome components, ribosomal RNA (rRNA) and ribosomal proteins (r-proteins), in this chapter, we focus on the nucleolus, the site for cytoplasmic ribosome biogenesis and assembly occurring in the light-microscopically visible structure of the cell nucleus. Similarly as in prokaryotes, for all higher organisms two ribosome subunits are preformed in the nucleolus, which are evolutionary conserved: the small 40S subunit (SSU) containing 18SrRNA, and the large 60S subunit containing 25/28S plus 5.8S and 5S rRNA. After export of the ribosome subunits (LSU) into the cytoplasm, the functionally active ribosome is associated with translatable mRNA to an 80S complex corresponding to the 70S structure in chloroplasts and prokaryotic cells.Following the ribozyme concept, ribosome subunits are built up by rRNA and r-proteins. The nuclear encoded rRNA genes (rDNA) are present as a multigene family in the genome, mostly located at the NOR (nucleolus-organizing region). In the transition area from fibrillar centers to the dense fibrillar component (FC/DFC) of the nucleolus, the 18S, 5.8S and 25S/28S rRNA are commonly transcribed by RNA polymerase I (pol I) as a large precursor, which in plants is approx. 35S in size (35S pre-rRNA); this 35Spre-rRNA is then stepwisely processed into the respective rRNAs. RNA polymerase III (pol III) transcribes the 5S rRNA component encoded by 5S

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Molecular Cell Biology: Different Transcriptional Activities in the Nucleus

1998

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Virtually the Entire Xenopus laevis rDNA Multikilobase Intergenic Spacer Serves to Stimulate Polymerase I Transcription

Cited by 26 publications

References 58 publications

Xenopus Ribosomal RNA Gene Intergenic Spacer Elements Conferring Transcriptional Enhancement and Nucleolar Dominance-like Competition in Oocytes

Xenopus Ribosomal RNA Gene Intergenic Spacer Elements Conferring Transcriptional Enhancement and Nucleolar Dominance-like Competition in Oocytes

Molecular Cell Biology: Organization and Molecular Evolution of rDNA, Nucleolar Dominance, and Nucleolus Structure

Molecular Cell Biology: Different Transcriptional Activities in the Nucleus

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