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  • 1
    Electronic Resource
    Electronic Resource
    Hexa- and pentapeptide extension of proalbumin: feedback inhibition of albumin synthesis by its propeptide in isolated hepatocytes and in the cell-free system (1982)
    s.l. : American Chemical Society
    Biochemistry 21 (1982), S. 6053-6059 
    Details
    ISSN: 1520-4995
    Source: ACS Legacy Archives
    Topics: Biology , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/bi00267a005
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  • 2
    Electronic Resource
    Electronic Resource
    Unusual heteromorphic sex chromosomes in a marsupial frog (1983)
    Springer
    Cellular and molecular life sciences 39 (1983), S. 1153-1155 
    Details
    ISSN: 1420-9071
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Heteromorphic sex chromosomes of the XY/XX-type were found in the karyotypes of the South American marsupial frogGastrotheca riobambae (Anura, Hylidae). The Y chromosome is considerably larger than the X chromosome and almost completely heterochromatic. The only nucleolus organizer region is localized in the X chromosome; this leads to a sex-specific difference in the number of nucleolus organizers. In the male meiosis, X- and Y chromosomes form a sex bivalent which can be readily distinguished from the autosomal bivalents.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01943157
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  • 3
    Electronic Resource
    Electronic Resource
    An oscillation data collection system for high-resolution protein crystallography (1981)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 37 (1981), S. 701-710 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: An oscillation data collection system for protein crystallography is described. The system consists of a modified Enraf-Nonius precession camera with cylindrical cassette, and stepping motor driven by a flexible microprocessor control system. The X-ray source is graphite-monochromatized radiation from an Elliott GX-21 rotating-anode generator run at 5.5 kW on a focal spot measuring 0.5 × 5.0 mm. The potential advantages of using a relatively large focal spot in conjunction with a graphite monochromator are discussed. Conditions for optimum collimation and X-ray intensity are considered, and it is shown that appropriately designed collimators with adjustable apertures can have substantial advantages over commercially available pinhole collimators. The oscillation films are processed by a procedure based on that of Rossmann [J. Appl. Cryst. (1979), 12, 225-238]. Determination of the initial alignment of the film is facilitated by a pair of reference pins incorporated in the cylindrical cassette. These pins ensure that the position of the film in the cassette is known, and avoid the need for fiducial marks. The crystal alignment and film measurement technique is fully automatic, requiring no prior input other than the approximate starting orientation of the crystal, the approximate unit-cell dimensions, and the angular oscillation range. An alternative method for the determination of crystal orientation is proposed which has been found to be somewhat superior to that of Rossmann, especially for smaller unit cells.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0567739481001587
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  • 4
    Electronic Resource
    Electronic Resource
    The use of distamycin A in human lymphocyte cultures (1984)
    Springer
    Human genetics 〈Berlin〉 65 (1984), S. 377-384 
    Details
    ISSN: 1432-1203
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The effect of the oligopeptide antibiotic distamycin A on human lymphocyte cultures was examined. Distamycin A specifically inhibits the condensation of the Y heterochromatin and induces a fragile site in the chromosome 16 (band q22) in some individuals. The optimal culture conditions under which an undercondensation of the Y heterochromatin and an induction of the fragile site in 16q22 can be achieved by in vitro treatment of lymphocytes were determined. This also permits the use of distamycin A in routine diagnostics of human chromosomes. The use of this technique in the analysis of translocations involving the Y chromosome is presented. The distamycin A-DNA interaction and the different possible explanations for the distamycin A-induced undercondensations of the Y heterochromatin and fragile sites 16q22 are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00291563
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  • 5
    Electronic Resource
    Electronic Resource
    Satellited Y chromosomes: Structure, origin, and clinical significance (1984)
    Springer
    Human genetics 〈Berlin〉 67 (1984), S. 72-85 
    Details
    ISSN: 1432-1203
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Three cases of inherited satellited Y chromosomes (Yqs) were analysed using several cytogenetic techniques. The cytogenetic data of the 14 cases of Yqs chromosomes described to date were reviewed. All Yqs chromosomes carry an active nucleolus organizer region (NOR) in their long arm and must have developed from translocations involving the short arms of the acrocentric autosomes. The structure of the heterochromatic satellite region in the Yqs chromosomes shows conspicuous inter-familial differences; this permits the reconstruction of the translocations from which the various Yqs were derived. Some causal factors leading to the development of Yqs chromosomes are considered: the specific localization of the four satellite DNAs and highly methylated DNA sequences in the karyotype, and some new experimental data on the spatial arrangement of heterochromatic regions in interphase nuclei. These provide distinct evidence for a preferential involvement of the autosomes 15 and 22 in the translocations with the Y heterochromatin. All clinical reports documenting Yqs males born with malformations were reviewed. It appears that the presence of an extra NOR and NOR-associated heterochromatin in the Yqs chromosomes does not cause any phenotypic abnormalities (as long as the Y euchromatin is intact). The possibility that a Yqs chromosome predisposes to non-disjunction and/or to translocations of other chromosomes is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00270562
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  • 6
    Electronic Resource
    Electronic Resource
    5-Azacytidine-induced undercondensations in human chromosomes (1984)
    Springer
    Human genetics 〈Berlin〉 67 (1984), S. 257-263 
    Details
    ISSN: 1432-1203
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The cytosine analogue 5-azacytidine induces very distinct undercondensations in human chromosomes if applied to lymphocyte cultures. The number of induced undercondensations and their chromosomal localization can be varied by the 5-azacytidine dose and the treatment time. “Pulverized” chromosomes or undercondensations in the G-band-positive chromosome regions are produced with high doses and long treatment times. If applied in low doses during the last hours of culture, 5-azacytidine induces specific undercondensations in the heterochromatin of chromosomes 1, 9, 15, 16, and Y. Optimum conditions required for inducing the various types of undercondensation in the chromosomes were determined. Various examples of the use 5-azacytidine in the analysis of chromosome rearrangements involving heterochromatic regions are presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00291352
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  • 7
    Electronic Resource
    Electronic Resource
    A frog with highly evolved sex chromosomes (1981)
    Springer
    Cellular and molecular life sciences 37 (1981), S. 243-245 
    Details
    ISSN: 1420-9071
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Highly differentiated ZZ/ZW sex chromosomes and an exceptionally low genome, size were found in the karyotypes ofPyxicephalus adspersus (Anura, Ranidae). The W-chromosome is considerably smaller than the Z-chromosome and consists to a very great proportion of constitutive heterochromatin. The DNA content of this species and the chromosome length have the lowest values determined in the Ranidae to date.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01991633
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  • 8
    Electronic Resource
    Electronic Resource
    Chromosome banding in amphibia (1980)
    Springer
    Chromosoma 80 (1980), S. 69-96 
    Details
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Highly differentiated heteromorphic sex chromosomes were found in the karyotypes of Pyxicephalus adspersus (= Rana adspersa) and analysed with the various banding methods. The W chromosome is considerably smaller than the Z chromosome and consists to a great proportion of constitutive heterochromatin. The chromosome lengths and the DNA content of this species have the lowest values determined in the Ranidae to date. The nucleolus organizer regions in the chromosomes reveal a high frequency of inter-individual variations (duplications, triplications) and aberrations. In one female animal, a translocation between the W chromosome and a nucleolus organizer was identified. Preliminary results indicate, that the same chromosome pair which in P. adspersus constitutes the heteromorphic sex chromosomes is still in an initial stage of morphological differentiation in P. delalandii. Although the ZZ/ZW sex chromosomes in Pyxicephalus have developed independently of the ZZ/ZW sex chromosomes in birds and reptiles, they seemed to have passed through identical stages of morphological differentiation. In this process, the heterochromatinization of the W chromosome had a decisive function.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00327567
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  • 9
    Electronic Resource
    Electronic Resource
    Evolutionary conservation of a common pattern of activity of nucleolus organizers during spermatogenesis in vertebrates (1982)
    Springer
    Chromosoma 86 (1982), S. 149-179 
    Details
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The patterns of activity of the nucleolus organizer regions (NORs) in the spermatogeneses of ten species of all non-mammalian classes of vertebrates and one species of the cephalochordates were investigated with the silver (Ag)-staining technique. The Ag-stainability of the NORs is a measure of the transcriptional activity of the ribosomal RNA genes. In all species, there is a very similar pattern of NOR-activity in the various stages of Spermatogenesis. The qualitative analysis of the Ag-stainability of the NORs was in very good agreement with the results obtained for mammals: Ag-stained NORs are detectable during the entire meiotic prophase up to the pachytene stage, completely absent in the meiotic metaphases I and II, and again demonstrable in early spermatid nuclei. The results confirm the occurrence of postmeiotic reactivation of the RNA genes. The preferential inhibition of rRNA synthesis by low doses of actinomycin D induced a rapid decline of the Ag-stainability of the postmeiotically reactivated NORs. The significance of the evolutionary conservation of the postmeiotic NOR-reactivation is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00288674
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  • 10
    Electronic Resource
    Electronic Resource
    Chromosome banding in Amphibia (1982)
    Springer
    Chromosoma 87 (1982), S. 327-344 
    Details
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The structure of the nucleolus organizer regions (NORs) in mitotic chromosomes, diploid nuclei and spermatogenesis was studied in 260 individual animals from 23 genera of the Anura. The analyses were performed with conventional cytogenetic methods as well as with Ag-staining, GC- and AT-specific fluorochromes (mithramycin, chromomycin A3, quinacrine) and C-banding. Most of the species have only one pair of NORs in their karyotypes. The majority of individuals of all species exhibited considerable differences in the sizes of their homologous NORs. Most of these heteromorphisms are due to tandem duplications or triplications in one of the two NORs. However, duplicated or triplicated NORs never occur in a homozygous form, but are instead always in combination with a normal-structured NOR in the homologous chromosome. In three animals, a complete deletion of one NOR and its closely associated constitutive heterochromatin was determined. The cytochemistry of the specific NOR-stainings are discussed. The size differences of the Ag-, mithramycin- and chromomycin A3-stained NORs can be traced to differences in the rDNA content in these NORs.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00327634
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