Enhancer-like properties of the 60/81 bp elements in the ribosomal gene spacer of Xenopus laevis

Labhart, Paul; Reeder, Ronald H.

doi:10.1016/0092-8674(84)90324-6

Cited by 208 publications

(198 citation statements)

References 23 publications

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“…In addition, we have reported that sequences in the intergenic spacer region of the Xenopus laevis ribosomal genes have enhancer-like activity on the RNA polymerase I promoter that directs transcription of the 7.5 kilobase rRNA precursor (4). The observation that promoters for RNA polymerase I as well as for RNA polymerase II utilize enhancers strengthens the idea that enhancers perform a vital function that may turn out to be required by all eukaryotic promoters.…”

Section: Introductionsupporting

confidence: 49%

“…Most of our experiments have been done with a block of ten of these 60/81bp repeats which we employ as an enhancer cassette. '40, * 52, pXlr4Ol, and pXlr521 have been described previously (4).…”

Section: Resultsmentioning

confidence: 99%

“…Oocyte injections were performed as described previously (3,4). All plasmids were injected in the presence of 500ug/ml aAmanitin.…”

Section: Methodsmentioning

confidence: 99%

“…3, lanes 5 and 6). Lane 4 shows that the transcription we detect past the HindIII site is truly promoter dependent (and not due to some nonspecific background transcription) since a plasmid similar to pXlr401 that has a promoter deletion (see lane 1) but contains an enhancer shows no transcription in this region. We can conclude from this result that no polymerases terminate within the enhancer region in pXlr4O7.…”

Section: Pxlr4olmentioning

confidence: 99%

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Xenopusribosomal gene enhancers function when inserted inside the gene they enhance

Labhart

Reeder

1985

Nucl Acids Res

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The ribosomal DNA of Xenopus laevis contains repeated sequence elements in the intergenic spacer region that enhance transcription from the adjacent gene promoter (1,2). Previous work has shown that these RNA polymerase I enhancers influence the target promoter when they are in either orientation, at a distance of several kilobases, and only when they are in cis (3-5). In this work, we further show that enhancer activity is unaffected by inserting the enhancers within the transcription unit whose promoter is being enhanced.In addition, enhancer activity does not interfere with transcription through its sequences. The results suggest that the enhancers act at a point prior to the initiation of transcription and that they are likely to be dispensable once transcription has begun.

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Section: Introductionsupporting

confidence: 49%

Section: Resultsmentioning

confidence: 99%

“…Oocyte injections were performed as described previously (3,4). All plasmids were injected in the presence of 500ug/ml aAmanitin.…”

Section: Methodsmentioning

confidence: 99%

Section: Pxlr4olmentioning

confidence: 99%

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Xenopusribosomal gene enhancers function when inserted inside the gene they enhance

Labhart

Reeder

1985

Nucl Acids Res

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“…Blocks of 60/81-bp repeats in the intergenic spacer of Xenopus ribosomal genes function as transcriptional enhancers (Labhart and Reeder 1984) and are among the best characterized UBF-binding sites. UBF binds cooperatively to these Xenopus Enhancer (XEn) elements Putnam and Pikaard 1992) and is required for enhancer function (McStay et al 1997).…”

Section: Generation and Mapping Of Heterologous Ubf-binding Site Arraysmentioning

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.

164

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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Spacers and processing of large ribosomal RNAs in Escherichia coli and mouse cells

et al. 1985

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The formation of mature large rRNAs from larger primary transcripts is very different in bacterial and mammalian cells. In both, cotranscription can help to assure the coordinated production of various rRNA species. However, in bacteria, processing is ordered, initiated by cleavages at double‐stranded stems which enclose the mature sequences; several cleavages are required to produce each mature terminus; and the final steps occur in polysomes, apparently linked to continued protein synthesis. In mouse cells, in contrast, cleavages generate nearly all mature termini stochastically and directly, with no evidence for double‐stranded stems as cleavage signals; and processing occurs in the nucleolus, long before any new rRNA chains arrive in polysomes. Spacer sequences also serve different potnetial functions at the evolutionary extremes. In bacteria, transcribed spacer sequences are associated with different secondary structures in the pre‐rRNA compared to the mature rRNA, and these may promote ribosome formation. In mammalian cells, analyses are too premature to assign any comparable function to transcribed spacer sequences, but the non‐transcribed spacers are probably critical in the organization and replication of nucleoli, functions that are absent from bacteria.

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Enhancer-like properties of the 60/81 bp elements in the ribosomal gene spacer of Xenopus laevis

Cited by 208 publications

References 23 publications

Xenopusribosomal gene enhancers function when inserted inside the gene they enhance

Xenopusribosomal gene enhancers function when inserted inside the gene they enhance

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

Spacers and processing of large ribosomal RNAs in Escherichia coli and mouse cells

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