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  • 1
    Electronic Resource
    Electronic Resource
    Chromosome fibers studied by a spreading technique (1966)
    Springer
    Chromosoma 20 (1966), S. 221-233 
    Details
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Chromosomes and interphase nuclei can be spread on the surface of water in a simplified Langmuir trough. Interphase nuclei of Triturus erythrocytes display fibers with a diameter of about 250–300 Å. Very similar fibers are seen in metaphase chromosomes of cultured human cells. Fibers from grasshopper spermatocyte chromosomes (prophase) are more variable in diameter, and many fibers thinner than 200 Å extend laterally from the chromosome. In the grasshopper spermatocyte, fibers align in parallel to form plates. It is suggested that the 250–300 Å fibers may represent an inactive state of the chromosome material, and that only the thinner fibers are involved in RNA synthesis. The 250–300 Å fibers may result from the folding or coiling of a thinner fiber having the approximate dimensions of the nucleohistone molecule.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00335209
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  • 2
    Electronic Resource
    Electronic Resource
    Gene amplification in the oocytes of dytiscid water beetles (1969)
    Springer
    Chromosoma 26 (1969), S. 169-187 
    Details
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract A conspicuous mass of extrachromosomal DNA (Giardina's body) is found in oogonia and oocytes of Dytiscid water beetles. Since in older oocytes this DNA is associated with numerous nucleoli, it seemed probable that the ovary might contain extra copies of the genes for ribosomal RNA (rRNA). This hypothesis has been confirmed by centrifugation and molecular hybridization studies. —In Dytiscus marginalis and Colymbetes fuscus a high density satellite DNA is found in somatic cells and in sperm. Hybridization experiments show that all of the rDNA, i.e., those sequences complementary to rRNA, are located in this satellite, although quantitatively they make up only a small fraction of the satellite. In both species the DNA isolated from ovariole tips is enriched with respect to the satellite. A parallel enrichment of the rDNA has been shown in ovariole tips of Colymbetes, but for technical reasons has not been examined in Dytiscus. —The following model is proposed. In somatic cells and sperm the rDNA is part of an extensive region of high density DNA in one or more chromosomes. In oogonia and oocytes the entire high density region is replicated extrachromosomally and appears cytologically as Giardina's body.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00326453
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  • 3
    Electronic Resource
    Electronic Resource
    Cytological localization of DNA complementary to ribosomal RNA in polytene chromosomes of Diptera (1970)
    Springer
    Chromosoma 29 (1970), S. 268-290 
    Details
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Molecular hybridization of radioactive ribosomal RNA with the DNA of cytological preparations is used to study the distribution of the ribosomal cistrons within the polytene chromosomes of three species of Diptera. It is shown that in Drosophila hydei the ribosomal cistrons are located within the nucleolus. In Rhynchosciara hollaenderi and Sciara coprophila, DNA coding for ribosomal RNA is present both in the nucleolus organizer regions of the chromosomes and in micronucleoli scattered throughout the nucleus. The DNA puffs in the salivary chromosomes of these sciarid flies do not contain detectable quantities of ribosomal cistrons. — RNA prepared by in vitro transcription has also been used to localize the ribosomal cistrons in Rhynchosciara. — Modifications in the technique of cytological hybridization are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00325943
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  • 4
    Electronic Resource
    Electronic Resource
    Satellite DNA associated with heterochromatin in Rhynchosciara (1971)
    Springer
    Chromosoma 32 (1971), S. 407-427 
    Details
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The DNA of Rhynchosciara hollaenderi was examined using isopycnic centrifugation in neutral CsCl. Two low density minor bands (collectively termed satellite DNA) were detected in addition to the main band DNA. Main band DNA has a buoyant density of 1.695 g/cm3. The larger of the two minor bands has a buoyant density of 1.680 g/cm3 while the smaller of the two minor bands has a buoyant density of about 1.675 g/cm3. Thermal denaturation studies have confirmed the presence of the two minor classes of DNA.—The satellite and main band DNAs were isolated in relatively pure form and were transcribed in vitro using DNA-dependent RNA polymerase from Escherichia coli. Annealing of the two complementary RNAs (cRNAs) with main band and satellite DNA was examined using filter hybridization techniques.—The chromosomal distribution of the satellite DNA was determined by in situ molecular hybridization of satellite-cRNA with Rhynchosciara salivary gland chromosomes. Satellite-cRNA hybridized with the centromeric heterochromatin of each of the four chromosomes (A, B, C, and X) and with certain densely staining bands in the telomere regions of the A and C chromosomes. Main band-cRNA annealed with many loci scattered throughout the chromosomes including areas containing satellite DNA.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00285252
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  • 5
    Electronic Resource
    Electronic Resource
    ”Micronucleoli” in the Xenopus germinal vesicle (1997)
    Springer
    Chromosoma 105 (1997), S. 438-443 
    Details
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract. The germinal vesicle of the Xenopus oocyte contains 1500 or more extrachromosomal nucleoli that are assembled on amplified copies of the rRNA genes. Many of these nucleoli have diameters of 10–15 μm, but some are much smaller, ranging down to 1 μm or less. Morphologically the smaller nucleoli or ”micronucleoli” resemble the similarly sized B snurposomes, but they can be recognized with appropriate antibody probes (e.g., anti-nucleolin and anti-fibrillarin). We describe here a sensitive fluorescent staining technique that uses avidin and propidium iodide to visualize the rDNA in the amplified nucleoli. Many large nucleoli stain about as brightly as haploid yeast nuclei on the same slides. They presumably contain about 12 Mb of DNA, equivalent to 900 rDNA repeats. The smallest micronucleoli display only a tiny dot of stain, which must correspond to relatively few rDNA repeats.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004120050205
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  • 6
    Electronic Resource
    Electronic Resource
    Kinetics of Deoxyribonuclease Action on Chromosomes (1963)
    [s.l.] : Nature Publishing Group
    Nature 198 (1963), S. 36-38 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] THE fine structure of chromosomes remains an enigma JL despite detailed knowledge about their component molecules. There is general agreement, based primarily on evidence from electron microscopy., that chromosomes contain delicate fibres of about 100 A diameter1, and the assumption is widely made ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/198036a0
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  • 7
    Electronic Resource
    Electronic Resource
    Structure of Mitochondrial Dna From Paramecium Tetraurelia (1980)
    Oxford, UK : Blackwell Publishing Ltd
    The @journal of eukaryotic microbiology 27 (1980), S. 0 
    Details
    ISSN: 1550-7408
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Mitochondrial DNA (mtDNA) from endosymbiote-free stocks of Paramecium tetraurelia was isolated by 2 procedures. the buoyant density of the mtDNA in neutral CsCI was 1.702 gm/cm3. a value consistent with the melting temperature of the mtDNA. Only linear molecules were observed by electron microscopy. These molecules were homogeneous in size with a monomer molecular weight of 25.6 × 106 daltons. the size of the mtDNA determined after digestion with the restriction endonucleases EcoRI or Hind III agreed with the value obtained by electron microscopy. These studies also revealed that the digestion pattern of mtDNA from stock 172 differed from that of the other 3 stocks (51, 127. 203) examined. Some mtDNA molecules exhibited snapback reassociation following denaturation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1550-7408.1980.tb04687.x
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  • 8
    Electronic Resource
    Electronic Resource
    Alteration of the Tetrahymena Genome During Nuclear Differentiation*† (1979)
    Oxford, UK : Blackwell Publishing Ltd
    The @journal of eukaryotic microbiology 26 (1979), S. 0 
    Details
    ISSN: 1550-7408
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Synopsis.The DNA of the macro- and the micronucleus of Tetrahymena thermophila has been compared by various biochemical methods. It became evident from their thermal denaturation temperatures and buoyant densities that the 2 DNAs were very similar in overall composition. Small differences were detected when the sequence complexities of these DNAs were compared by DNA renaturation studies. The studies suggested that ˜ 10% of the micronuclear genome was lost or underrepresented in the macronucleus. Comparison of individual gene levels revealed further differences. By using the technic of gene cloning a micronuclear sequence was isolated which hybridized only with micronuclear, but not with macronuclear DNA. These results indicated the occurrence of elimination or underreplication of this sequence in the macronucleus. Gene amplification was also shown to occur. In the micronucleus only a single copy of rDNA was found integrated into the chromosome. During macro-nuclear development, amplification was observed to occur, and the amount of rDNA to increase, until there were ˜ 200 copies per haploid genome in the mature macronucleus. all of them extrachromosomal and palindromic. The 3rd case of alteration involved a simple repeated sequence, (CCCCAA)n, present in the termini of rDNA and also in many other locations of the genome. Restriction endonuclease digestion studies revealed drastic differences in the organization of the repeats between macro-and micronucleus. These differences may be interpreted as the results of chromosome fragmentation which occurs at every cluster of the repeats during macronuclear development. The relationship between this event and gene amplification and elimination is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1550-7408.1979.tb02723.x
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  • 9
    Electronic Resource
    Electronic Resource
    CAJAL BODIES: The First 100 Years (2000)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Cell and Developmental Biology 16 (2000), S. 273-300 
    Details
    ISSN: 1081-0706
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Biology , Medicine
    Notes: Abstract Cajal bodies are small nuclear organelles first described nearly 100 years ago by Ramon y Cajal in vertebrate neural tissues. They have since been found in a variety of animal and plant nuclei, suggesting that they are involved in basic cellular processes. Cajal bodies contain a marker protein of unknown function, p80-coilin, and many components involved in transcription and processing of nuclear RNAs. Among these are the three eukaryotic RNA polymerases and factors required for transcribing and processing their respective nuclear transcripts: mRNA, rRNA, and pol III transcripts. A model is discussed in which Cajal bodies are the sites for preassembly of transcriptosomes, unitary particles involved in transcription and processing of RNA. A parallel is drawn to the nucleolus and the preassembly of ribosomes, which are unitary particles involved in translation of proteins.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1146/annurev.cellbio.16.1.273
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  • 10
    Electronic Resource
    Electronic Resource
    Through the looking glass (2006)
    [s.l.] : Nature Publishing Group
    Nature medicine 12 (2006), S. 1142-1145 
    Details
    ISSN: 1546-170X
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Medicine
    Notes: [Auszug] After much urging, my parents bought me a microscope when I was 14 years old, not one of the toys I had struggled with up to that time, but the real thing, with crystal-sharp images and an oil immersion objective (Fig. 1). Once I was hooked on the vast world that lay beyond what I could see with my ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/nm1006-1142
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