title: Mutational specificity of 1,3-bis-(2-chloroethyl)-1-nitrosourea in a Chinese hamster ovary cell line.
abstract: The mutational specificity of the alkylating agent 1-3-bis-(2-chloroethyl)-1-nitrosourea (BCNU) was analyzed at the endogenous hemizygous adenine phosphoribosyl transferase gene of the Chinese hamster ovary cell line D422. A 1-h treatment of the Chinese hamster ovary cells with 50 microM BCNU resulted in a toxicity level of 62% and induced mutation at this target with a frequency of 32.1 mutants/10(6) survivors (6-fold above background). Analysis of 49 BCNU-induced mutants at the DNA sequence level revealed that BCNU induced primarily base substitutions. The predominant BCNU-induced mutations were G:C----T:A transversions, which comprised 51% (25 of 49) of the mutations; while G:C----A:T transitions, expected from miscoding of O6-alkylguanine, represented only 16.3% (8 of 49) of the mutants recovered. This result was not anticipated, since Chinese hamster ovary cells are deficient in O6-alkylguanine-DNA alkyltransferase, which should render them especially sensitive to O6-alkylguanine-mediated mutations. It was also notable that two "hotspots" for BCNU-induced G:C----T:A transversions were observed, which involved different surrounding DNA sequences but similar helix parameters when analyzed by an application of Calladine's Rules. Possible mechanisms for the observed BCNU-induced mutations are presented.
authors.affiliation: Department of Environmental Health Sciences, University Hospitals, Case Western Reserve University, Cleveland, Ohio 44106.
authors.forename: D T
authors.initials: DT
authors.lastname: Minnick
authors.forename: M L
authors.initials: ML
authors.lastname: Veigl
authors.forename: W D
authors.initials: WD
authors.lastname: Sedwick
mesh_terms: D000228:Adenine Phosphoribosyltransferase / Q000235:genetics*; D000818:Animals; D001483:Base Sequence; D016466:CHO Cells / Q000201:enzymology; D002330:Carmustine / Q000633:toxicity*; D002470:Cell Survival / Q000187:drug effects; D006224:Cricetinae; D005796:Genes; D008780:Methyltransferases / Q000378:metabolism; D008969:Molecular Sequence Data; D016296:Mutagenesis; D019853:O(6)-Methylguanine-DNA Methyltransferase
chemical_list: D008780:Methyltransferases; D019853:O(6)-Methylguanine-DNA Methyltransferase; D000228:Adenine Phosphoribosyltransferase; D002330:Carmustine