Relative argininosuccinate synthetase mRNA levels and gene copy number in canavanine-resistant lymphoblasts.
Mutants resistant to the arginine analogue, canavanine, have been isolated from two normal lymphoblast lines, MGL8B2 and MGL33. These mutants constitutively express up to 200-fold higher amounts of structurally normal argininosuccinate synthetase, the urea cycle enzyme that converts citrulline to argininosuccinate. Relative levels of argininosuccinate synthetase mRNA were compared among normal and canavanine-resistant lines using in vitro translation of poly(adenylic acid) RNA and blot hybridization of total cytoplasmic RNA to an argininosuccinate synthetase cDNA. Both of these approaches indicated that the canavanine-resistant lines contain increased steady-state levels of synthetase-specific mRNA relative to their sensitive parents and that these were roughly correlated with levels of enzyme activity. Blot hybridization of EcoRI-digested genomic DNA preparations revealed no detectable differences in argininosuccinate synthetase structural gene copy number between normal and canavanine-resistant lymphoblasts, demonstrating that the canavanine-resistant phenotype is not caused by gene amplification.
D001124:Argininosuccinate Synthase / Q000235:genetics*; D002172:Canavanine / Q000494:pharmacology*; D002460:Cell Line; D004351:Drug Resistance; D005796:Genes; D006801:Humans; D008025:Ligases / Q000235:genetics*; D008214:Lymphocytes / Q000502:physiology*; D014176:Protein Biosynthesis; D012333:RNA, Messenger / Q000235:genetics*
D012333:RNA, Messenger; D002172:Canavanine; D008025:Ligases; D001124:Argininosuccinate Synthase