Isolation and Analysis of Chinese Hamster Cells Carrying Forward and Reverse Mutations in the Hypoxanthine-Guanine Phosphoribosyltransferase Locus
In studies of somatic cell genetics, mutagenesis, cell fusion, etc., the locus for hypoxanthine-guanine phosphoribosyltransferase (HGPRT) has received considerable attention (see Caskey and Kruh for a review1). The product of this gene in various mammalian systems is a protein of about 25,000 molecular weight which associates into oligomers that catalyze the formation of IMP or GMP from 5-phosphoribosyl pyrophosphate (PP-Ribose-P) plus hypoxanthine or guanine. A number of purine analogs such as 8-azaguanine and 6-thioguanine also serve as substrates for the enzyme and are converted to toxic nucleotides which kill normal cells and enable the isolation of HGPRT-deficient clones of cultured cells(2). Although the enzyme is normally not required for cell growth, agents such as aminopterin can be used to block de_ novo synthesis of purine nucleotides thus making cellular multiplication dependent on the presence of hypoxanthine and HGPRT activity and providing a reverse selective system for the locus(3). The realization that HGPRT-deficiency is the biochemical defect in human patients with the X-linked Lesch-Nyhan Syndrome(4) localized the locus for the enzyme to the X chromosome and focused additional attention on the gene and its product.
KeywordsChinese Hamster Cell Reverse Mutation Mouse Neuroblastoma Cell Somatic Cell Genetic HPRT Locus
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