title: Isolation of somatic cell mutants with specified alterations in hypoxanthine phosphoribosyltransferase.
abstract: Cellular resistance to 6-thioguanine is almost always associated with a complete loss of hypoxanthine phosphoribosyltransferase (HPRT) activity, while resistance to 8-azaguanine has frequently been shown to occur independently of any changes in the HPRT activity. As a result, mutant cells selected for resistance to 6-thioguanine are also resistant to 8-azaguanine, but cells selected for 8-azaguanine resistance are not necessarily cross-resistant to 6-thioguanine. Our previous studies demonstrated that this difference is due to differential utilization of the two purine analogs by HPRT in the cells. In this paper we describe a novel selective procedure for the systematic isolation of cellular mutants that contain wild-type levels of HPRT, are sensitive to 6-thioguanine, and yet are able to survive in medium containing both HAT and a high level of 8-azaguanine. We also present evidence which shows that such mutants arise through a mutation that specifically alters the HPRT molecule so that the enzyme no longer recognizes 8-azaguanine as a substrate, while remaining catalytically functional with hypoxanthine and 6-thioguanine. Mutants of this type may be useful as a marker in gene-transfer experiments.
mesh_terms: D000818:Animals; D001375:Azaguanine / Q000494:pharmacology*; D002460:Cell Line; D004351:Drug Resistance; D005020:Ethyl Methanesulfonate / Q000494:pharmacology; D005796:Genes / Q000187:drug effects; D007041:Hypoxanthine Phosphoribosyltransferase / Q000235:genetics*; D008769:Methylnitronitrosoguanidine / Q000494:pharmacology; D051379:Mice; D013866:Thioguanine / Q000494:pharmacology*
chemical_list: D008769:Methylnitronitrosoguanidine; D005020:Ethyl Methanesulfonate; D007041:Hypoxanthine Phosphoribosyltransferase; D013866:Thioguanine; D001375:Azaguanine