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At least 19 recordsLinked to original sources
PubMed1979

Isolation and organization of calf ribosomal DNA.

Ribosomal DNA (rDNA) from calf was isolated by three density gradient centrifugations. The first centrifugation in Cs2S04/BAMD was used to obtain partially resolved dG+dC-rich fractions from total DNA. The second and third centrifugations, in Cs2S04/Ag+, led to the isolation of an rDNA fraction characterized by a symmetrical band in CsCl, p = 1.724 g/cm3. This new procedure appears to be generally suitable for the isolation of rDNA and other dG+dC-rich repeated genes. The organization of isolated calf rDNA has been studied by restriction enzyme digestion and by hybridization with cloned rDNA from Xenopus laevis. The repeat unit of calf rDNA has a molecular weight of 21x10(6) and is split by EcoR1 into two fragments, 16x10(6) and 5.0x10(6), and by BamHI into seven fragments. EcoRI and BamHI sites have been mapped. Most of the 18S and 28S RNA genes and the transcribed spacer are contained in the small EcoRI fragment, while the non-transcribed spacer is localized in the large EcoRI fragment. This spacer showed length heterogeneity within a single individual; such heterogeneity is limited to two regions of the spacer.

Animals↗
PubMed1978

The fate of DNA satellites I, II, III and ribosomal DNA in a familial dicentric chromosome 13:14.

In a family with a stable dicentric 13:14 translocation chromosome, the distribution of DNA sequences complementary to satellite DNAs I, II and III and ribosomal RNA were studied. The translocation chromosome showed a loss of sequences complementary to all three satellite DNAs, located in the short arms of the acrocentric chromosomes, but slightly more of the sequences complementary to satellite I were retained than of the other two satellite DNAs. The fact that material was lost from all three satellites indicates that they are not present as single discrete blocks in these chromosomes, when we would expect to find the distal sequences lost and the proximal ones retained, but consist of interspersed blocks with each sequence represented by more than one, and probably several blocks. There was a total loss of ribosomal DNA from the nucleolar organiser regions of the chromosomes involved in the 13:14 translocation, but an interesting finding was the presence of extra ribosomal DNA and satellite DNAs I, II and III in one chromosome 22 which was found in seven out of nine individuals of the family with the 13:14 translocation, and in only one of five individuals without the translocation. There may be a compensatory mechanism present when certain sequences are elminated during chromosomal rearrangements. The relationship of such mechanisms to reproductive fitness is discussed.

Base Sequence↗
PubMed1978

Characterization of two types of yeast ribosomal DNA genes.

The intragenic organization of ribosomal DNA from a diploid strain of Saccharomyces cerevisiae was analyzed by using recombinant DNA molecules constructed in vitro. Restriction analysis of the yeast ribosomal DNA with the EcoRI restriction enzyme indicated that eight restriction fragments were present in the ribosomal DNA of this strain: X' (1.87 X 10(6) daltons), A (1.77 X 10(6) daltons), B (1.48 X 10(6) daltons), C (1.22 X 10(6) daltons), D (0.39 X 10(6) daltons), E (0.36 X 10(6) daltons), F (0.22 X 10(6) daltons), and G (0.17 X 10(6) daltons). These fragments were distributed between two different types of ribosomal DNA genes, which had the restriction maps: (formula: see text) in which the underlined region shows the repeating unit. The diploid yeast strain contained approximately equal amounts of each of these two types of genes. The analysis of the recombinant DNA molecules also indicated that the yeast ribosomal genes are homogeneous and extensively clustered.

DNA↗
PubMed2025

Chromosome-specific epigenetic control and transmission of ribosomal DNA arrays in Hominidae genomes.

Ribosomal RNA (rRNA) genes are organized in tandem arrays known as ribosomal DNA (rDNA) on multiple chromosomes in Hominidae genomes. We measured copy number and transcriptional activity status of rRNA gene arrays across multiple individual genomes, revealing an identifiable fingerprint of rDNA copy number and activity. In some cases, entire arrays were transcriptionally silent, characterized by high DNA methylation across the rRNA gene, inaccessible chromatin, and the absence of transcription factors and transcripts. Silent arrays showed reduced association with the nucleolus and decreased interchromosomal interactions, consistent with the model that nucleolar organizer function depends on transcriptional activity. Removing rDNA methylation activated silent arrays. Array activity status remained stable through induced pluripotent stem cell reprogramming and differentiation into cerebral and intestinal organoids. Haplotype tracing in two unrelated family trios showed paternal transmission of silent arrays. We propose that the epigenetic state buffers rRNA gene dosage, specifies nucleolar organizer function, and can propagate transgenerationally.

Epigenesis, Genetic↗
PubMed1979

Extrachromosomal circular ribosomal DNA in the yeast Saccharomyces carlsbergensis.

Purified ribosomal DNA from Saccharomyces carlsbergensis contains a small proportion of circular DNA molecules with a contour length of 3 micron or integral multiples thereof. Hybridization of yeast ribosomal DNA with 26 S rRNA, using the R-loop technique, reveals that these circular molecules contain sequences complementary to yeast ribosomal RNA. We suggest that these extrachromosomal rRNA genes may be intermediates in the amplification of rRNA genes in yeast.

DNA, Circular↗
PubMed1977

Simple Mendelian inheritance of the reiterated ribosomal DNA of yeast.

A diploid strain of yeast (Saccharomyces cerevisiae) was found to be heterozygous for two forms of the highly repetitious ribosomal DNA. These forms could be distinguished by the pattern of fragments produced after digestion with the site-specific restriction endonuclease EcoRI. The mode of inheritance of ribosomal DNA was determined by tetrad analysis. Of 14 tetrads analyzed, 12 clearly showed the ribosomal DNA forms segregating as a single Mendelian unit. The simplest interpretation of this result is that all of the approximately 100 copies of the ribosomal DNA genes of the yeast cell are located on one chromosome and that meiotic recombination within these genes is suppressed. Two of the 14 tetrads showed the segregation patterns expected as the result of mitotic recombination within the ribosomal DNA.

Base Sequence↗
PubMed1979

Deletions, rearrangements and tandem duplications of recombinant plasmids containing yeast ribosomal DNA.

Recombinant DNA plasmids, formed by the insertion of yeast ribosomal DNA into Escherichia coli plasmids pSC101 or pMB9, underwent deletions, rearrangements and tandem duplications. Independently derived deletion products of plasmids, constructed using pMB9 as a vector, are indistinguishable from each other. These deletion products from multimers composed of tandem repeats. In at least one case a plasmid, constructed by inserting an SmaI fragment of yeast ribosomal DNA into pSC101, underwent deletion and rearrangement to form a product in which a segment, consisting of part of the pSC101 sequence and part of the yeast ribosomal DNA sequence, was duplicated to form a tandem repeat. Deletion and rearrangement take place in Rec+, recA- and recB- recC- cells. The rate of deletion in Rec+ cells is higher than in recA- cells. The rate of deletion in minicell-producing, X-ray resistant strains is much higher than in other Rec+ strains.

Chromosome Deletion↗
PubMed1979

The organization of a nuclear DNA sequence from a higher plant: molecular cloning and characterization of soybean ribosomal DNA.

The recombinant DNA vector, lambda Charon 4A, was used to construct a library of DNA sequences from the genomic DNA of soybean (Glycine max). To define the organization of ribosomal DNA (rDNA) in the soybean genome, clones containing sequences complementary to both 17S and 25S rRNA have been isolated from this library and used in conjunction with Southern blot hybridization. The rRNA genes are tandemly reiterated with a relatively small unit repeat length of 7.8 kb. There is no heterogeneity in the length of the rDNA repeat units although they display limited differences in either base sequence or pattern of methylation. The cloned rDNA sequences are shown to comprise the entire repeat unit and have been used to obtain a detailed restriction map as well as an approximate transcription map of soybean rRNA genes. The cloning of rDNA from soybean suggests that recombinant DNA techniques can be successfully applied to the genomic DNA of higher plants despite the high degree of methylation exhibited by plant DNA.

Bacteriophage lambda↗
PubMed1978

Molecular analysis of cloned human 18S ribosomal DNA segments.

A fraction of DNA from the human fetal lung fibroblast line IMR-90, 30-fold enriched for ribosomal DNA, was cloned in the lambda phage vector Charon 16A. Of 978 clones assayed by hybridization to a mixture of 125I-labeled 18S and 28S ribosomal RNA, 11 recombinants containing a 3.8-megadalton segment of human 18S ribosomal DNA were identified. Restriction endonuclease analysis of these clones demonstrated variation only in orientation of the human gene segment within the phage vector. Restriction sites that we had previously detected from analysis of restriction products of unfractionated human DNA by using the Southern transfer method were also present in the cloned DNA segment. Recombinant DNA technology thus provides a valid and efficient means to define structural conservation or variation within families of human genes.

Cell Line↗
PubMed1979

Restriction analysis of spacers in ribosomal DNA of Drosophila melanogaster.

The sequence arrangement of ribosomal DNA (rDNA) spacers in Drosophila melanogaster was analyzed with restriction endonucleases. Spacers, derived from cloned rDNA repeats and from uncloned purified rDNA, are internally repetitive, as demonstrated by the regular 250 base pairs interval between sites recognized by the enzyme Alu I. Length heterogeneity of spacers is due at least in part to varying numbers of repeated sequence elements. All spacers and analyzed, whether derived from X or from Y chromosomal rDNA, have a very similar sequence organization. The distance separating the repeated nontranscribed spacer sequences from the 5' end of the transcribed region is conserved in all ten cloned fragments examined, and is probably less than 150 base pairs, as measured by electron microscopy.

Animals↗
PubMed2024

Ribosomal DNA copy number variation associates with hematological profiles and renal function in the UK Biobank.

The phenotypic impact of genetic variation of repetitive features in the human genome is currently understudied. One such feature is the multi-copy 47S ribosomal DNA (rDNA) that codes for rRNA components of the ribosome. Here, we present an analysis of rDNA copy number (CN) variation in the UK Biobank (UKB). From the first release of UKB whole-genome sequencing (WGS) data, a discovery analysis in White British individuals reveals that rDNA CN associates with altered counts of specific blood cell subtypes, such as neutrophils, and with the estimated glomerular filtration rate, a marker of kidney function. Similar trends are observed in other ancestries. A range of analyses argue against reverse causality or common confounder effects, and all core results replicate in the second UKB WGS release. Our work demonstrates that rDNA CN is a genetic influence on trait variance in humans.

Humans↗
PubMed1978

Heterogeneity in Chinese hamster ribosomal DNA.

A discrete heterogeneity has been detected in Chinese hamster ribosomal DNA after Eco R1 digestion of total DNA followed by a Southern transfer and hybridization with [125I]18S or [125I]28S ribosomal RNA. Digestion with Eco R1 produces three fragments, 4.3, 6.0 and 9.5 x 10(6) daltons respectively, which hybridize with 18S RNA. The smallest fragment also hybridizes with 28S RNA. Either length heterogeneity or sequence heterogeneity (i.e. presence of an additional Eco R1 site in some of the rDNA molecules) must be invoked to account for the two larger Eco R1 fragments that contain 18S but not 28S sequences. Eco R1 and Hind III maps, consistent with either length or sequence heterogeneity, are presented. The data at this time, however, do not distinguish between the two alternatives.

Animals↗
PubMed1977

Construction and restriction endonuclease mapping of hybrid plasmids containing Saccharomyces cerevisiae ribosomal DNA.

Fragments produced by partial digestion of Saccharomyces cerevisiae ribosomal DNA (rDNA) with the restriction endonuclease EcoRI were ligated in vitro to the bacterial plasmid RSF2124. The resulting hybrid plasmids were cloned in Escherichia coli. Three hybrid plasmids which contain at least one intact repetitive unit of the multiple, tandem sequences of the yeast rDNA genes have been further characterized. These plasmids have been used to construct a map of the EcoRI, SmaI, HindII and HindIII restriction sites in the individual repetitive units of yeast rDNA.

DNA↗
PubMedDate not supplied

Heat and alkali induced hyperchromic effects in the ribosomal DNA of sea urchin (Lytechinus variegatus) sperm.

Melting point dispersion analysis of the ribosomal DNA (rDNA) of sea urchin (Lytechinus variegatus) sperm shows a scatter in the Tm obtained at wavelengths of 230-280 nm at 5 nm intervals. The dispersion curve of the rDNA, which lies in between human thymus DNA and T2 DNA, is probably suggestive of the intragenic heterogeneity. Alkali induced hyperchromic effects, examined over 220-290 nm at 5 nm intervals, show that the hyperchromic effect is minimum at 250 nm, followed by a sharp increase around 270-275 nm. These findings are consistent with the hyperchromic effects produced by alkali-melted G + C--rich DNA of lower organisms.

Alkalies↗