Showing papers on "Ribosomal DNA published in 1973"
TL;DR: In situ hybridization of 5S RNA and cRNA transcribed in vitro from Xenopus laevis5S DNA shows that 5S DNA is localized at or near the telomere region of the long arm of many, if not all, of the X. laevIS chromosomes, which suggests that the uniformity of5S sequences on non-homologous chromosomes might be maintained by crossing-over between the chromosomes.
Abstract: In situ hybridization of 5S RNA and cRNA transcribed in vitro from Xenopus laevis 5S DNA shows that 5S DNA is localized at or near the telomere region of the long arm of many, if not all, of the X. laevis chromosomes. No 5S DNA is detected near the nucleolus organizer in the normal X. laevis chromosome complement, but in a X. laevis kidney cell line, 5S DNA is found at the distal end of the secondary constriction. The arrangement of 5S DNA in several types of interphase nuclei is described. — During the pairing stages of meiosis the telomeres of most or perhaps all of the chromosomes become closely associated so that the regions containing 5S DNA form a single cluster. This close association might be either a cause or a result of the presence of the similar sequences of 5S DNA on many telomeres. It suggests that the uniformity of 5S sequences on non-homologous chromosomes might be maintained by crossing-over between the chromosomes.
190 citations
TL;DR: Observations suggest that somatic variations in rDNA content may involve independent polytenization of the nucleolus organizer without change in the number of ribosomal cistrons per organizer.
Abstract: The saturation values for ribosomal RNA hybridization have been determined for DNA from diploid and polytene tissues of Drosophila melanogaster. These values have been measured in XO and XX larvae which have, respectively, one and two nucleolus organizers in the diploid chromosome set. The results show that (1) in diploid cells the ribosomal (r)DNA is present in amounts proportional to the number of nucleolus organizers, (2) in polytene cells the rDNA is under-replicated with respect to the euchromatic DNA, and (3) in polytene cells the amount of rDNA is independent of the diploid number of nucleolus organizers. These observations suggest that somatic variations in rDNA content may involve independent polytenization of the nucleolus organizer without change in the number of ribosomal cistrons per organizer. The independent polytenization of rDNA is proposed as the chromosomal explanation for the relative increase in rDNA in flies of the XO constitution.
151 citations
TL;DR: Under appropriate genetic conditions, it appears that disproportionate rDNA replication can be generated at the level of both somatic and germ line cells.
Abstract: The ribosomal RNA (rRNA) genes of Drosophila melanogaster can undergo a disproportionate replication of their number. This occurs when the cluster of rRNA genes (rDNA) of one chromosome is maintained with a homologous chromosome that is completely or partially deficient in its rDNA. Under appropriate genetic conditions, it appears that disproportionate rDNA replication can be generated at the level of both somatic and germ line cells. In the latter case, mutants partially deficient for rDNA can increase their rRNA gene number to the wild type level and transmit this new genotype to successive generations.
137 citations
TL;DR: Ribosomal RNA synthesized by hybrid frogs from the cross between Xenopus laevis and Xenopus mulleri was analyzed by molecular hybridization with purified ribosomal DNA from each species to show that in hybrid frogs X. mulleri rDNA is repressed regardless of which species is the female parent.
126 citations
TL;DR: Calculations indicate that the linear density of polymerase molecules on the ribosomal DNA template increases with the bacterial growth rate, such that in rapidly growing bacteria all Ribosomal RNA genes are nearly saturated with RNA polymerase.
76 citations
TL;DR: The genes for rRNA were found to resist melting at temperatures 10° or more above the Tm, which permits enrichment of these genes by thermal fractionation.
Abstract: Extract: Quantitation of human genes for ribosomal RNA (rRNA) was possible by molecular DNA/RNA hybridization on nitrocellulose discs. Labeled ribosomal RNA hybridizes with an average of 14 × 10-5 of the total human DNA. If we assume that the diploid cell contains 5.5 × 1012 daltons of DNA, the ribosomal RNA hybridizes with 7.7 × 108 daltons of ribosomal DNA (rDNA), which is equal to about 320 genes. Hybridization of rRNA with DNA of three different diploid sources shows a rRNA/DNA ratio which varies from 12–15.4 × 10-5. The rRNA/DNA ratio of DNA derived from trisomy 21 cells is not significantly different from the normal cells. The genes for rRNA were found to resist melting at temperatures 10° or more above the Tm. This property permits enrichment of these genes by thermal fractionation. Speculation: Ribosomal RNA genes are probably present on several human chromosomes. The ability to enrich these genes in relation to the whole human DNA indicates that they are clustered.
62 citations
TL;DR: The generality of the organization of transcribing rDNA, another amplified rDNA system, is examined, in order to examine the extrachromosomal DNA masses which occur in the oocytes of diverse insects and constitute a considerable amount of the total nuclear DNA.
Abstract: The DNA molecules which contain the cistrons for ribosomal RNA (rDNA) consist of repeats of alternating segments of (i) regions which are transcribed into the primary rRNA precursors (pre-rRNA) and (ii) regions which are either not transcribed (corresponding to “spacers” sensu Miller and Beatty1) or might be, perhaps in parts, transcribed into RNA molecules which, however, are not covalently. linked with pre-rRNA (“spacers” sensu Reeder and Brown2 ; for demonstration of partial transcripts from spacers see Scheer et al.3). The relative arrangement of the “spacer” units and the stretches coding for pre-rRNA (corresponding to the matrix units of Miller and Beatty1,4) has been elucidated by different methods in chromosomal and extrachromosomal rDNA of diverse amphibian species, including urodeles and anurans1,3–13. In the clawed toads, Xenopus laevis and X. muelleri, according to differential DNA denaturation studies12,13, this pattern of arrangement is identical in both chromosomal (“nucleolus organizer”) and extrachromosomal (“amplified”) rDNA. Extrachromosomal nucleolar material consisting of the actively transcribing amplified rDNA is especially suitable for biochemical and electron microscopic studies because it provides a natural enrichment of this kind of DNA in a state which is topologically isolated from all the other chromatin. We have therefore chosen, in order to examine the generality of the organization of transcribing rDNA, another amplified rDNA system, the extrachromosomal DNA masses which occur in the oocytes of diverse insects and constitute a considerable amount of the total nuclear DNA (for example, 59% in Tipula oleracea14, 23–35% in Dytiscid beetles15 and 14–31% in Acheta domesticus 16–19 ). As has been shown by numerous authors18,20–24 a favourable material in this respect is the house cricket, A. domesticus.
60 citations
TL;DR: In this article, the amount of rDNA in a strain monosomic (2 n − 1) for chromosome I with a related diploid (2 2 n ) strain was compared.
44 citations
TL;DR: The genes for cytoplasmic ribosomal RNA are partially resolved from the bulk of the DNA by CsCl equilibrium centrifugation, and in some plants the buoyant density of the ribosomic RNA genes is as expected from the base composition of ribosome RNA.
Abstract: The genes for cytoplasmic ribosomal RNA are partially resolved from the bulk of the DNA by CsCl equilibrium centrifugation. Although in some plants the buoyant density of the ribosomal RNA genes is as expected from the base composition of ribosomal RNA, others show a large discrepancy which cannot be due to the presence of low G-C spacer-DNA. The cross-hybridization observed with 1.3 and 0.7 × 106 molecular weight ribosomal RNAs and DNA, which varies greatly with different plant species, is not due to contamination of the ribosomal RNAs, and is specific for the ribosomal DNA of each species, probably largely restricted to those sequences coding for the two stable ribosomal RNAs. The double reciprocal plot may be used for the extrapolation of saturation values only with caution, because in these cases such plots are not linear over the whole of the hybridization reaction.
44 citations
TL;DR: Several lines of evidence support the hypothesis that short duplex segments are formed by out-of-register renaturation of the 16 S + 23 S ribosomal RNA genes (rDNA) of B. subtilis, and linkage groups containing seven or nine rDNA sets separated by spacer DNA's are proposed.
34 citations
01 Jan 1973
TL;DR: In the DNA of the cricket Achetu domesticus there is a DNA satellite with a buoyant density of 1.716 g/ml, which contains the genes for 28s and 18s RNA and the DNA non-homologous to ribosomal RNA (called the “spacer” DNA) as discussed by the authors.
Abstract: In the DNA of the cricket Achetu domesticus there is a DNA satellite with a buoyant density of 1.716 g/ml, which contains the genes for 28s and 18s RNA and the DNA non-homologous to ribosomal RNA (called the “spacer” DNA). These two components constitute the ribosomal DNA. Complementary RNA was synthesized in vitro with Escherichiu coli RNA polymerase, using as a template the high buoyant density DNA satellite isolated from CsCl gradient fractions (ribosomal DNA). The complementary HS-RNA of high specific activity was then hybridized to squashed oocyte pachytene chromosomes. As the denaturation agent of the DNA, 90 yo formamide in 0.1 XSSC was used, since it best preserved the structure of the fragile pachytene chromosomes. Cytologically the DNA amplification is mainly localized in the major chromomeres of chromosomes 6 and 11 which, together, contain 26.3 % of the total nuclear oocyte DNA. The hybridization with complementary RNA shows that the silver grains are mainly localized in these two major chromomeres. Since the amount of DNA in the major chromomeres of chromosomes 6 and 11 at early pachytene is 2.00 and 1.48 pg respectively, the ratio number of silver grains/amount of DNA turns out to be 46.2 and 35.4 respectively, whereas the corresponding value for the rest of the complement is 2.4. Thus, the present evidence makes it possible to locate the ribosomal DNA in single chromosomes and in single chromomeres of the Achetu complement.
TL;DR: In genetic combinations undergoing ribosomal DNA magnification, the frequency of crossing-over between X and Y chromosomes is increased at least 20-fold above that in similar combinations not undergoing magnification.
Abstract: In genetic combinations undergoing ribosomal DNA magnification, the frequency of crossing-over between X and Y chromosomes is increased at least 20-fold above that in similar combinations not undergoing magnification. Such recombination occurs at the ribosomal DNA level. The data are consistent with a model where extra copies of ribosomal DNA are formed which, after circularization, are integrated into the chromosome.
TL;DR: It is concluded that rDNAs of normal X and Y chromosomes have opposite orientation with respect to the centromere and the implications of this observation are discussed.
Abstract: We tested for recombination within the DNA that codes for ribosomal RNA (rDNA) on the X and Y chromosomes of Drosophila melanogaster. The criterion was the appearance of intermediate bb alleles on X-Y recombinants from wild bb+ and lethal bb1 loci carried on parental chromosomes. Recombination within the rDNA occurs only when the rDNA of the X chromosome is inverted. We conclude that rDNAs of normal X and Y chromosomes have opposite orientation with respect to the centromere. The implications of this observation are discussed.
TL;DR: The results suggest that human rRNA genes are located exclusively on the chromosomes of the groups D and G and that all these chromosomes contain r RNA genes.
Abstract: Clonal derivatives of a human heteroploid cell line, with different numbers of acrocentric chromosomes, show different rDNA contents. A linear relationship has been found between the rDNA content and the relative mass of the acrocentric chromosomes (D+G) expressed as the ratio between the mass of their DNA and the mass of the DNA of the whole chromosomal complement. The results suggest that human rRNA genes are located exclusively on the chromosomes of the groups D and G and that all these chromosomes contain rRNA genes.
DOI•
01 Jan 1973TL;DR: Recent studies of the amplification mechanism by autoradiography of isolated rDNA using both light and electron microscopy are summarized.
Abstract: In somatic cells the DNA coding for 28S and 18S ribosomal RNA (rRNA) is confined to the chromosomal nucleolus organizer (Birnstiel et al., 1966). However, in oocytes from a wide variety of animals, this nucleolar DNA is selectively amplified and accumulated in the nucleus free of the chromosomes (Gall, 1969). In Xenopus laevis, the best studied example, almost three-quarters of the nuclear DNA in a diplotene oocyte codes exclusively for ribosomal RNA (Brown and Dawid, 1968). The extra ribosomal DNA (rDNA) is synthesized during a three-week period in early meiotic prophase (Gall, 1968; Macgregor, 1968; Bird and Birnstiel, 1971; Watson-Coggins and Gall, 1971) and during diplotene it forms hundreds of extrachromosomal nucleoli, which actively engage in rRNA synthesis (Miller and Beatty, 1969). This paper will summarize our recent studies of the amplification mechanism by autoradiography of isolated rDNA using both light and electron microscopy.
TL;DR: Ribosomal RNA cistrons are replicated more rapidly than the remainder of the genome in the late embryonic or earliest larval stages, but more slowly during the later cycles of DNA synthesis in those larval tissues which develop high levels of polyteny.
TL;DR: The major chromomeres of pachytene chromosomes 6 and 11 in the oocytes of Acheta (Orthoptera) are regions of amplification for ribosomal RNA cistrons (28 S and 18 S).
Abstract: The major chromomeres of pachytene chromosomes 6 and 11 in the oocytes of Acheta (Orthoptera) are regions of amplification for ribosomal RNA cistrons (28 S and 18 S). During late prophase the amplified DNA copies are released from the chromomeres, which decrease in size as the amount of DNA decreases. The number of nucleotide pairs released from the major chromomere of chromosome 11 is about 1.38 × 109.
TL;DR: Drosophila melanogaster embryos that lacked ribosomal DNA were obtained from appropriate crosses and cells taken from such embryos before overt differentiation took place differentiated into neurons and myocytes with the same success as did wild-type controls.
Abstract: Drosophila melanogaster embryos that lacked ribosomal DNA were obtained from appropriate crosses. Cells were taken from such embryos before overt differentiation took place and were cultured in vitro. These cells differentiated into neurons and myocytes with the same success as did wild-type controls. Therefore, ribosomal RNA synthesis is not necessary for the differentiation of neurons and myocytes in vitro.