Biochemical genetics of Chinese hamster cell mutants with deviant purine metabolism: isolation, selection, and characterization of a mutant lacking hypoxanthine-guanine phosphoribosyltransferase activity by nutritional means.

Mutants of the Chinese hamster ovary cell derived from CHO-K1 have been selected for lack of hypoxanthine-guanine phosphoribosyltransferase (EC 2.4.2.8) (HGPRT) without the use of a drug-resistance protocol. The procedure depends on the use of a parental strain carrying a mutation making it unable to synthetize purines and thus dependent upon exogenously added purines for growth. The standard "BUdR-visible-light" procedure is then used to select those cells which can use adenine but cannot use hypoxanthine as a purine source. These cells are shown to be thioguanine resistant, to be unable to incorporate exogenously added hypoxanthine into purine nucleotides, to complement our other adenine-specific purine auxotrophs, Ade-H and Ade-I but not to complement a cell isolated by virtue of thioguanine resistance, and to lack the activity of HGPRT. The use of such multiply marked mutants and cells related to them for further analysis of purine nucleotide biosynthesis and interconversion is discussed.