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Spontaneous frequency of 6‐thioguanine resistant mutants in CHO‐AS52 cells after prolonged culturing in the absence of selective agents
Author(s) -
Li Albert P.
Publication year - 1990
Publication title -
environmental and molecular mutagenesis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1
H-Index - 87
eISSN - 1098-2280
pISSN - 0893-6692
DOI - 10.1002/em.2850150407
Subject(s) - chinese hamster ovary cell , mutant , hypoxanthine guanine phosphoribosyltransferase , cloning (programming) , aminopterin , microbiology and biotechnology , genotoxicity , biology , xanthine , gene , genetics , cell culture , biochemistry , medicine , immunology , enzyme , methotrexate , toxicity , computer science , programming language
The Escherichia coli xanthine‐guanine phosphoribosyl transferase (XPT) containing Chinese hamster ovary (CHO‐AS52) cells were studied in our laboratory to evaluate its general applicability in genotoxicity testing of industrial chemicals. Our initial effort was to evaluate the stability of the 6‐thioguanine sensitive phenotype. The CHO‐AS52 cells were cloned and cultured continuously for over 600 days in the absence of any selective agents. The spontaneous 6‐thioguanine resistant mutant frequency was quantified periodically. The frequency was found to increase continuously with time from approximately 20 × 10 −6 to a plateau of approximately 250 × 10 −6 in 122 days. The mutant frequency fluctuated around the plateau value up to the last day of our study, at 648 days after cloning. A similar observation was made for cells that were recloned or treated with aminopterin (to selectively kill 6‐TG resistant mutants) at approximately 450 days after the initial cloning. Our data suggest that the xpt gene was stably incorporated in the CHO cells.