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  • 1
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Mutants of mouse L-cells which are temperature-sensitive for growth have been obtained by using both selective and nonselective isolation procedures on populations treated with the mutagen nitrosoguanidine. Selective isolation was carried out by utilizing a five-day treatment with 3H-TdR and ara-C as selective agents at the nonpermissive temperature. Nonselective isolation was performed by isolating 1400 clones in the absence of selective agents and then testing them for temperature-sensitivity. From this experiment we obtained a minimum estimate of 6 × 10-3 for the frequency of mutants in the mutagentreated population. The mutants were characterized by their plating efficiencies, growth in suspension culture, and uptake of isotopic precursors of DNA, RNA, and protein. A range in phenotypes was observed, and there appeared to be some differences between the mutants obtained by the two types of isolation procedures. In uptake experiments the most marked reductions in the rates of precursor incorporation were seen with 3H-TdR, rather than 3H-UR or 3H-Leu. Different mutant lines showed considerable variation in the rate of cessation of DNA synthesis as well as the time required for termination of cell division. These experiments suggest that both types of isolation procedures are feasible for obtaining temperature-sensitive mutants having a range of phenotypes.
    Additional Material: 2 Ill.
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 98 (1979), S. 327-339 
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Nine spontaneous and seven ethyl methanesulfonate induced revertants of the Chinese hamster ovary cell line mutant (tsHl), which possesses a temperature sensitive leucyl-tRNA synthetase, were isolated and characterized with respect to growth rate, leucyl-tRNA synthetase activity and thermolability, intracellular leucine pool size, and rRNA content. Although most revertants had increased leucyl-tRNA synthetase activity, and of those tested, all but one had increased thermostability, each appears to be unique. One revertant may be an intergenic suppressor since it appears to contain an elevated level of tsHl-like synthetase. There was no evidence for any of the revertants having increased rRNA and tRNA contents, however, many showed leucine pools two to three times larger than wild type cells. Since similar increases have been observed in tsHl cells they are believed to result from regulation of leucine pool size by the leucyl-tRNA synthetase and are of a magnitude sufficient to affect significantly the growth of revertants at 38.5°C.
    Additional Material: 4 Ill.
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