Sequence organization of the spacer DNA in a ribosomal gene unit of Xenopus laevis

Boseley, Paul; Moss, Tom; Mächler, M.; Portmann, Rudolf; Birnstiel, Max L.

doi:10.1016/0092-8674(79)90291-5

Cited by 218 publications

(110 citation statements)

References 29 publications

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“…This variation presumably reflects an equilibrium between mutation, homogenisation and selection. This situation is similar to that found in Xenopus where regions of about 130 bp in the NTS are found to be homologous to the promoter region around the transcription initiation site (7,8,9,22). The presence of multiple initiation-like sequences in the NTS of genera as distinct as Xenopus and Drosophila suggests that the arrangement is of functional significance.…”

Section: Construction Of Clonessupporting

confidence: 67%

“…The overall features of NTS structure described here are therefore common to several Drosophila species. Interestingly, a number of regions with different periodicities has also been described in the NTS's of species of Xenopus (7) and may prove to be a general feature of eukaryotes.…”

Section: Construction Of Clonesmentioning

confidence: 99%

“…Secondly, it has been shown that cell-free extracts of a particular species will only transcribe rDNA from that same species and not from a different species (3,6). Thus Nucleic Acids Research tive initiation regions in the NTS which are highly homologous to the region around the rDNA transcription initiation site ( 7,8,9). Microinjection experiments have recently demonstrated that such regions may enhance rDNA transcription in Xenopus, (T. Moss, pers.…”

Section: Introductionmentioning

confidence: 99%

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Multiple Pol I initiation sequences in rDNA spacers ofDrosophila melanogaster

1982

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Section: Construction Of Clonessupporting

confidence: 67%

Section: Construction Of Clonesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Multiple Pol I initiation sequences in rDNA spacers ofDrosophila melanogaster

1982

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“…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).…”

mentioning

confidence: 76%

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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“…The Xenopus laevis ribosomal gene enhancers occur as clusters of repetitive elements that are either 60 or 81bp in length (14). Most of our experiments have been done with a block of ten of these 60/81bp repeats which we employ as an enhancer cassette.…”

Section: Resultsmentioning

confidence: 99%

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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Sequence organization of the spacer DNA in a ribosomal gene unit of Xenopus laevis

Cited by 218 publications

References 29 publications

Multiple Pol I initiation sequences in rDNA spacers ofDrosophila melanogaster

Multiple Pol I initiation sequences in rDNA spacers ofDrosophila melanogaster

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

Xenopusribosomal gene enhancers function when inserted inside the gene they enhance

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