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  • 1
    Electronic Resource
    Electronic Resource
    Subclonal heterogeneity of the multidrug resistance phenotype in a cell line expressing antisense MDR1 RNA (1994)
    Springer
    Somatic cell and molecular genetics 20 (1994), S. 463-480 
    Details
    ISSN: 1572-9931
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract A multidrug resistant (MDR) cell line was transfected with an antisense MDR1 expression vector and transfectant clones were analyzed for reversion of the MDR phenotype. Only one of 10 antisense-expressing transfectants showed a reduction in drug resistance, MDR1 mRNA and P-glycoprotein. Observations made using rhodamine-123, a fluorescent substrate for P-glycoprotein, revealed that dye retention in individual cells was highly variable within this antisense-expressing clone. Subpopulations were established from the original clone based on differences in rhodamine-123 retention. Rhodamine-123 retention varied inversely with levels of P-glycoprotein and MDR1 mRNA. All subpopulations expressed similar levels of antisense MDR1 RNA yet had dramatic differences in MDR1 mRNA levels. Analysis of vector integration site restriction fragment length polymorphisms confirmed that all populations originated from the same transfectant clone. Nuclear run-on analysis indicated that themdr1 gene is transcribed at the same rate in all populations, suggesting that the reduction in MDR1 mRNA is mediated posttranscriptionally. Cells with the greatest reduction in MDR1 mRNA accumulate distinct antisense RNA transcripts in the nuclear RNA fraction, suggesting that antisense effectiveness in this system is associated with a nuclear event or process. These results reveal that antisense RNA activity is not necessarily distributed equally within a clonal populations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02255838
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  • 2
    Electronic Resource
    Electronic Resource
    Characterization of dominant hamster cell mutants resistant to oxygenated sterols (1982)
    Springer
    Somatic cell and molecular genetics 8 (1982), S. 557-574 
    Details
    ISSN: 1572-9931
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Stable mutants of Dede and CHO cells, resistant to suppression of cholesterogenesis by oxygenated sterols, have been isolated in a single step. Luria-Delbrück fluctuation analysis indicated a random occurrence of resistance at a rate of 1×10 −7 mutations/cell/generation. Cholesterol biosynthesis, 3-hydroxy-3-methylglutaryl coenzyme A reductase activity, and growth of the mutant cells were coordinately resistant to oxygenated sterols in the culture medium, and this resistance was expressed as a dominant traint in somatic cell hybrids of the wild-type and mutant cells. The dominant resistance was employed in the selection of various cell hybrids. There was complete additivity of reductase activities in mixed lysates of inhibited wild-type and uninhibited mutant cells, indicating that cytosolic (in)activation factors were not causative of this resistance. We suggest that oxygenated sterols are (co)repressors in suppression of the synthesis of the reductase and that the resistance mutant phenotypes result from altered regulatory loci.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01542851
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  • 3
    Electronic Resource
    Electronic Resource
    Chromosome-mediated gene transfer of HPRT and APRT in an intraspecific human cell system (1983)
    Springer
    Somatic cell and molecular genetics 9 (1983), S. 175-188 
    Details
    ISSN: 1572-9931
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Chromosome-mediated transfer of genes between human cell lines was accomplished using HeLa cells as chromosome donors and HT1080 fibrosarcoma lines as recipients. This report describes the intraspecific transfer of two genetic markers, hypoxanthine-guanine-phosphoribosyl-transferase (HPRT +)and adenine phosphoribosyltransferase (APRT +).The isolation and characterization of the necessary enzyme-deficient (HPRT − and APRT −)recipient HT1080 cell lines are also described. The chromosome-mediated gene transfer was carried out using a modification of the procedure of Miller and Ruddle, including treatment of the donor chromosomes with calcium phosphate and subsequent exposure of the recipient cells of dimethyl sulfoxide. In experiments to optimize this procedure for HT1080 cell recipients, we found that a brief (2-min) exposure to high DMSO concentration (20%) was effective for enhancing transfer efficiencies in this system. Transfer frequencies (transferents per recipient cells assayed) averaged approximately 1×10−6 for HPRT + and were 〉2×10−6 for APRT +.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01543176
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  • 4
    Electronic Resource
    Electronic Resource
    Soldier-specific chemicals of the termiteCurvitermes strictinasus Mathews (Isoptera, Nasutitermitinae) (1981)
    Springer
    Journal of chemical ecology 7 (1981), S. 127-133 
    Details
    ISSN: 1573-1561
    Keywords: Isoptera ; Nasutitermitinae ; isolation ; identification ; Curvitermes strictinasus (Mathews) ; defense secretion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract The defense secretion of the soldier termites ofCurvitermes strictinasus Mathews has been analyzed. Seven components have been isolated and identified, including limonene, terpinolene,p-cymen-8-ol, tridecan-2-one, tridecen-2-onecis,trans-farnesal, andtrans,trans-farnesal.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00988640
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  • 5
    Electronic Resource
    Electronic Resource
    Chemical composition of the frontal gland secretion ofSyntermes soldiers (Isoptera, Termitidae) (1981)
    Springer
    Journal of chemical ecology 7 (1981), S. 135-145 
    Details
    ISSN: 1573-1561
    Keywords: Isoptera ; Nasutitermitinae ; Syntermes species ; defensive secretion ; isolation ; identification ; terpenoid compounds
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract The defensive secretions from the frontal glands of soldier termites of the genusSyntermes contain similar mixtures of mono- and sesquiterpene hydrocarbons. The major components inS. dirus, S. molestus, S. brevimalatus, S. peruanus, and a new species (Syntermes sp. n), iscis-β-ocimene. A substantial amount of aristolochene is found inSyntermes sp. n. and is present at lower levels in all the other species;S. brevimalatus contains onlycis-β-ocimene and aristolochene. The four other species also contain minor amounts of epi-α-selinene and germacrene A. The latter compound has been identified on the basis of its rearrangement product β-elemene. The termiteS. grandis differed markedly from the otherSyntermes species in that no terpenoid components were found in the soldier extract. With the obvious exception ofS. grandis, the same soldier-specific mono- and sesquiterpenes occurred in all species. The total amount of secretion per unit weight of soldiers varies with the species and is inversely proportional to the development of the mandibular apparatus. InS. molestus smaller gland size is compensated for by a greater number of soldiers foraging trails.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00988641
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  • 6
    Electronic Resource
    Electronic Resource
    Chromosome-mediated transfer of murine alleles for hypoxanthine-guanine phosphoribosyl transferase (HGPRT) and ouabain resistance into human cell lines (1985)
    Springer
    Biochemical genetics 23 (1985), S. 1-15 
    Details
    ISSN: 1573-4927
    Keywords: chromosome-mediated gene transfer ; hypoxanthine-guanine phosphoribosyl transferase (HGPRT) ; ouabain resistance ; HT 1080 fibrosarcoma cells
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Genetic drug-resistance markers were transferred via purified metaphase chromosomes from mouse L cells into the human fibrosarcoma line HT1080 and HeLa S3 cells. Interspecific chromosome-mediated transfer of hypoxanthine-guanine phosphoribosyl transferase (HGPRT; EC 2.4.2.8) from mouse L cells into HGPRT− HT1080 cells occurred at a frequency of approximately 1×10−7. The presence of the mouse allele for HGPRT in transferent isolates was confirmed by isoelectric focusing. Transfer of ouabain resistance from mouse L cells to HT1080 and HeLa S3 cells occurred at an average frequency of approximately 4×10−7. Expression of the mouse trait in transferent isolates was confirmed by their ability to withstand doses of ouabain which would be lethal to spontaneous ouabain-resistant mutants of the human cells but not to mouse L cells. Ouabain-resistant transferents of human cells showed 104- to 〉105-fold enhanced drug resistance, characteristic of either wild-type or mutant alleles, respectively, from ouabain-resistant donor L cells. Unstable expression of the transferred phenotypes in the absence of selection was seen in some isolates, but expression was lost at slow rates.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00499108
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  • 7
    Electronic Resource
    Electronic Resource
    UV-Induced enhancement of recombination among lambda bacteriophages in UV-sensitive host bacteria (1967)
    Springer
    Molecular genetics and genomics 100 (1967), S. 166-177 
    Details
    ISSN: 1617-4623
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The UV enhancement of recombination among λ bacteriophages was studied in host bacteria that are defective in DNA repair and compared to that observed in wild type host strains. The following conclusions were drawn: 1. The UV enhancement of recombination is even greater in HCR− than in HCR+ host strains. The UV lesions that promote recombination are repaired by host cell reactivation with the same efficiency as are potentially lethal UV lesions. 2. The UV enhancement of λ recombination is the same in HCR+ host strains that are deficient in their own recombination as it is in the wild type hosts. 3. Very few lesions per phage particle are sufficient to stimulate the enhanced recombination. The UV-stimulated recombination occurs during the same time interval as host cell reactivation. 4. There is substantial multiplicity reactivation of UV lesions in λ. Similar numbers of recombination events neutralize similar numbers of UV lesions in HCR+ and HCR− hosts, but a much greater survival increase is observed in the latter.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00333603
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  • 8
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    Chromosome-mediated transfer of murine alleles for hypoxanthine-guanine phosphoribosyl transferase (HGPRT) and ouabain resistance into human cell lines (1985)
    Springer
    Details
    Publication Date: 1985-02-01
    Print ISSN: 0006-2928
    Electronic ISSN: 1573-4927
    Topics: Biology , Chemistry and Pharmacology
    Published by Springer
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