CHO/HGPRT mutagenicity assay. II. Genetic basis of 6-thioguanine resistance

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An essential aspect of any attempt to study mutation induction in mammalian cells is the demonstration that genetic alterations are the bases for the altered phenotypes. We have defined reproducible conditions for the selection of 6-thioguanine-resistant (TG/sup r) variants of Chinese hamster ovary (CHO) cells. It is known that many such variants contain altered forms of the enzyme hypoxanthine (Hx)-guanine phosphoribosyl transferase (HGPRT). Our question was whether every variant colony which develops under our conditions has properties consistent with a genetic alteration at the HGPRT locus. We considered other possible mechanisms for the TG resistance such as: (a) colony formation ... continued below

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Pages: 11

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O'; Neill, J P & Hsie, A W January 1, 1979.

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An essential aspect of any attempt to study mutation induction in mammalian cells is the demonstration that genetic alterations are the bases for the altered phenotypes. We have defined reproducible conditions for the selection of 6-thioguanine-resistant (TG/sup r) variants of Chinese hamster ovary (CHO) cells. It is known that many such variants contain altered forms of the enzyme hypoxanthine (Hx)-guanine phosphoribosyl transferase (HGPRT). Our question was whether every variant colony which develops under our conditions has properties consistent with a genetic alteration at the HGPRT locus. We considered other possible mechanisms for the TG resistance such as: (a) colony formation by wild-type cells which have escaped the toxic effects of TG as a result of the death of cells and release of purine bases and metabolites into the medium and/or as the result of depletion of medium TG due to inherent decay and cellular metabolism leading to a loss of selection stringency; (b) phenotypic resistance due to some transient, adaptive response in cellular physiology, such as increased rates of purine biosynthesis; (c) stable resistance as a result of mutations at other loci, such as alterations in TG uptake or alterations which affect intracellular levels of purine nucleotides or PRPP. Our conclusion from these studies is that the TG/sup r/ phenotype which is quantified by use of the CHO/HGPRT system does represent genetic alterations, and that we are performing quantitative mutagenesis is determinations with this system. (PCS)

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Pages: 11

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Dep. NTIS, PC A02/MF A01.

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  • Cold Spring Harbor symposium on quantitative mammalian cell mutagenesis and mutagen screening, Cold Springs Harbor, NY, USA, 6 May 1979

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  • Report No.: CONF-790537-3
  • Grant Number: W-7405-ENG-26
  • Office of Scientific & Technical Information Report Number: 6031479
  • Archival Resource Key: ark:/67531/metadc1098877

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  • January 1, 1979

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  • Feb. 18, 2018, 3:59 p.m.

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  • May 16, 2018, 1:05 p.m.

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O'; Neill, J P & Hsie, A W. CHO/HGPRT mutagenicity assay. II. Genetic basis of 6-thioguanine resistance, article, January 1, 1979; Tennessee. (digital.library.unt.edu/ark:/67531/metadc1098877/: accessed October 20, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.