Organization of the ribosomal RNA genes of dictyostelium discoideum: Mapping of the nontrascribed spacer regions

Cockburn, Andrew; Newkirk, Mary Jane; Firtel, Richard A.

doi:10.1016/0092-8674(76)90043-x

Cited by 76 publications

(15 citation statements)

References 6 publications

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“…The Tetrahymena genome contains several single 5S genes in addition to those clustered in tandem repeats. Except for Dictyostelium (37,38) and yeast (39, 40) where the 5S genes are linked to the large ribosomal genes, and Neurospora where mainly dispersed single copies of the 5S genes are found (34), a tandem repeat type of organization is common for these genes in eukaryotes (reviewed in 18, 41; see also 42). The single genes could be nontranscribed pseudogenes.…”

Section: Organization Of the 5s Genes In Tetrahymenamentioning

confidence: 99%

Sequence organization within and flanking clusters of 5S ribosomal RNA genes inTetrahymena

et al. 1984

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Macro- and micronuclei of Tetrahymena thermophila each contain approximately 30 clusters of 5S genes per haploid genome. Structural changes in DNA sequences associated with some of these clusters occur during the development of the transcriptionally active macronucleus from the transcriptionally inert micronucleus. Exonuclease digestion indicates that DNA fragmentation is not responsible for these changes, making it likely that sequence rearrangements occur near some 5S genes during macronuclear development. These rearrangements appear to be random in location with respect to the 5S genes and do not alter either the tandem repeat organization of the genes, the average number (five) or the range in number (one to about 16) of genes per cluster. The 5S gene clusters are not closely linked and are not flanked by common repeating elements large enough to cross-hybridize. Sequence analysis of one tandem repeat suggests that Tetrahymena 5S genes have intragenic promoters. These observations indicate that features other than DNA rearrangements or DNA sequence per se are responsible for the transcriptional activation of 5S genes during macronuclear development.

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Section: Organization Of the 5s Genes In Tetrahymenamentioning

confidence: 99%

Sequence organization within and flanking clusters of 5S ribosomal RNA genes inTetrahymena

et al. 1984

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“…There is extrachromosomal amplification of genes for rRNA (rDNA) in the oocytes of amphibia (1,2) and some insects (3,4) and in the ciliate protozoa Tetrahymena (5,6) and Paramecium (7). rDNA is also extrachromosomal in Physarum (8) and Dictyostelium (9). In Tetrahymena macronuclei (10) and in Physarum, rDNA is in the form of palindromic dimers.…”

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confidence: 99%

Macronuclear DNA of the hypotrichous ciliate Oxytricha fallax

Rae

Spear

1978

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

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DNA in the macronuclei of Oxytricha fallax, as in other hypotrichous ciliate protozoa, exists as small, achromosomal molecules rather than in chromosomes. We report studies on 0. fallax DNA using physicochemical procedures and nucleic acid hybridization. Macronuclear DNA molecules range in size from 22 kilobase pairs (kb) to about 0.5 kb. The DNA has a buoyant density in CsCl of 1.694 gcm-3 and a melting temperature in 15 mM NaCl/1.5 mM sodium citrate, pH 7, at 65.40. These values correspond to 34.7% Gua + Cyt and 28.1% Gua + Cyt, respectively, and base composition determined by thin-layer chromatography of nucleotides is 32.4% Gua + Cyt. The only modified nucleotide that is detectable is N6-methyldeoxyadenylate (0.2%), and the amount and kind of modification cannot account for the discrepancies in nucleotide composition determination by the three methods. The (rDNA) in the oocytes of amphibia (1, 2) and some insects (3, 4) and in the ciliate protozoa Tetrahymena (5, 6) and Paramecium (7). rDNA is also extrachromosomal in Physarum (8) and Dictyostelium (9). In Tetrahymena macronuclei (10) and in Physarum, rDNA is in the form of palindromic dimers. In Paramecium and other organisms, amplified genes for rRNA are tandemly repeated several to many times in extrachromosomal DNA molecules.Hypotrichous ciliate protozoa such as Oxytricha have a macronuclear genome comprised entirely of "extrachromosomal" or "achromosomal" DNA (11). These DNA pieces are produced by fragmentation of polytene chromosomes in postconjugative cells (12,13), and the process of macronuclear development from micronuclei results in considerable reduction in DNA sequence complexity (14). As was shown by Lawn and coworkers (15), macronuclear DNA is heterodisperse, but a particular DNA sequence in the macronucleus is found in a single size class of DNA molecules or in a small variety of discrete sizes.In this report, characteristics of the achromosomal macronuclear DNA of Oxytricha fallax are presented. 0. fallax is related to the unidentified species studied in Prescott's laboratory (15), but it is distinguished from the latter by its smaller size, by a different DNA buoyant density in CsCl, and by having two micronuclei per cell instead of four. Nevertheless, the processes of conjugation, macronuclear development, and vegetative reproduction in 0. fallax follow the general pattern described for other hypotrichs. Our reported studies on 0. fallax have concentrated on the genes for 25S and 19S rRNAs and for 5S rRNA. These genes have been localized to relatively small, nonpalindromic DNA, little larger than necessary to accomodate single coding sequences.MATERIALS AND METHODS Culture and In Vivo Labeling of 0. fallax. Cultures of 0. fallax were obtained from the Indiana University collection. Cells were grown in 0.1% Cerophyl medium with Chlamydonas reinhardtii as a food source. Medium was supplemented either with heat-killed Escherichia coli or with killed Klebsiella aerogenes in a vitamin/stigmasterol mixture (16). Cultures were harves...

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“…That 5 s rRNA, but not 4 s tRNA, was repressed in reconstructed slugs appears peculiar, in view of the fact that the syntheses of both RNAs in eukaryotic cells are catalyzed by one and the same enzyme, RNA polymerase I11 (23), whose existence in Dictyostelium cells has been shown as well (24,25). The reason for this preferential regulation of small molecular weight RNAs is unknown at present, but it may be related to the fact that the structure of Dictyostelium rDNA is unique in that 5 s rRNA coding region links to the stretch of 17s + 26s rRNA coding region (26,27), as observed in yeast and prokaryotes (28,29).…”

Section: Discussionmentioning

confidence: 96%

Repression of rRNA synthesis during slug reconstruction in Dictyostelium discoideum

Uchiyama¹

1987

Biochem. Cell Biol.

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When cells dissociated from "slugs" are allowed to reaggregate, they reconstruct slugs. During this process, the cells showed a marked decrease in the ratio of labeled RNA lacking poly(A) to labeled total RNA as compared with that of cells in normal slugs. Irrespective of the change in total labeled RNA, the ratio remained low even after 6 h of reconstruction. Sucrose density gradient analysis of RNA showed that the synthesis of high molecular weight rRNA (26S and 17S) was considerably repressed in reconstructed slugs as compared with normal slugs. Polyacrylamide gel electrophoresis of low molecular weight rRNA revealed that the synthesis of 5S rRNA, but not 4S tRNA, was repressed.

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Organization of the ribosomal RNA genes of dictyostelium discoideum: Mapping of the nontrascribed spacer regions

Cited by 76 publications

References 6 publications

Sequence organization within and flanking clusters of 5S ribosomal RNA genes inTetrahymena

Sequence organization within and flanking clusters of 5S ribosomal RNA genes inTetrahymena

Macronuclear DNA of the hypotrichous ciliate Oxytricha fallax

Repression of rRNA synthesis during slug reconstruction in Dictyostelium discoideum

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