title: Demonstration of normal and mutant protein M1 subunits of deoxyGTP-resistant ribonucleotide reductase from mutant mouse lymphoma cells.
abstract: From a mutagenized population of mouse T-lymphoma cells (S49) in continuous culture a cell line has been isolated (Ullman, B., Gudas, L. J., Clift, S. M., Martin, D. W., Jr. (1979) Proc. Natl. Acad. Sci. U. S. A. 76, 1074-1978) with ribonucleotide reductase activity that is inhibited only 50% by concentrations of dGTP which abolish wild type enzyme activity. Ribonucleotide reductase activity from this dGuo-L cell line retains its normal sensitivity to dATP. The partial sensitivity/partial resistance of the ribonucleotide reductase suggests that the dGuo-L cell line is heterozygous for ribonucleotide reductase, possessing one normal allele and one allele which codes for a dGTP-resistant enzyme. Both homologous and heterologous mixing experiments between the separated nonidentical subunits of ribonucleotide reductase, protein M1 and protein M2, from wild type and dGuo-L cells showed that the dGTP- feedback sensitivity was governed by the source of the protein M1. A partial resolution of two dGuo-L protein M1 components was achieved by chromatography on dextran blue-Sepharose. In order to resolve the two dGuo-L protein M1 components more completely, we introduced into dGuo-L cells a second mutation which conferred resistance of the ribonucleotide reductase to dATP, while the original dGTP resistance was maintained. The chromatography of protein M1 from this latter clone, dGuo-L-Aphid-G5, on dATP-Sepharose resolved two kinetically distinct protein M1 components. The first component was sensitive to dGTP inhibition but stimulated by dATP; the second was absolutely refractory to dGTP but sensitive to dATP inhibition. This confirms the hypothesis that the dGuo-L parent is heterozygous for protein M1, containing one wild type and one mutant allele.
mesh_terms: D000818:Animals; D002460:Cell Line; D003848:Deoxyguanine Nucleotides / Q000494:pharmacology*; D004351:Drug Resistance; D006579:Heterozygote; D007700:Kinetics; D008223:Lymphoma / Q000201:enzymology*; D046911:Macromolecular Substances; D051379:Mice; D009154:Mutation; D009374:Neoplasms, Experimental / Q000201:enzymology; D012264:Ribonucleotide Reductases / Q000235:genetics* / Q000302:isolation & purification / Q000378:metabolism
chemical_list: D003848:Deoxyguanine Nucleotides; D046911:Macromolecular Substances; C007257:2'-deoxyguanosine 5'-phosphate; D012264:Ribonucleotide Reductases