The nature of mutants induced by ionizing radiation in cultured hamster cells. II. Antigenic response and reverse mutation of HPRT-deficient mutants induced by gamma-rays or ethyl methanesulphonate.
A large series of independent mutants deficient in HPRT enzyme activity, isolated from V79-4 hamster cells (Brown and Thacker, 1984), were assessed for properties which reflect the nature of the genetic changes induced. A total of 88 mutants were screened, 43 isolated from gamma-ray-treated cultures and 45 induced by ethyl methanesulphonate (EMS). Firstly, each mutant was assayed for the presence of protein with the antigenic response of HPRT (cross-reacting material, CRM), using an antibody raised against partially purified V79-4 HPRT enzyme. In a competitive inhibition assay, 31% of EMS-induced mutants were CRM-positive compared to 7% of the gamma-ray series. Secondly, each mutant was tested for ability to revert to HPRT proficiency, either spontaneously or after treatment with the powerful mutagen ethyl nitrosourea (ENU). All except 2 of the EMS-induced mutants reverted with ENU, and many reverted spontaneously, under the given conditions. However reversion was not detected in about 80% of gamma-ray-induced mutants, suggesting that the types of forward mutation caused by ionizing radiation differ qualitatively from those caused by EMS. The EMS-induced mutations are likely to be mostly point mutations, with at least 40% of the missense type, while gamma-ray-induced mutations may arise mostly through larger genetic changes.
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Brown
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Stretch
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Thacker
D000818:Animals; D002460:Cell Line; D006224:Cricetinae; D003412:Cricetulus; D003429:Cross Reactions; D000939:Epitopes / Q000032:analysis*; D005020:Ethyl Methanesulfonate / Q000633:toxicity*; D005720:Gamma Rays; D007041:Hypoxanthine Phosphoribosyltransferase / Q000235:genetics* / Q000276:immunology; D009154:Mutation; D011233:Precipitin Tests
D000939:Epitopes; D005020:Ethyl Methanesulfonate; D007041:Hypoxanthine Phosphoribosyltransferase