title: Comparison of the mutagenicity and mutagen specificity of ethylenimine with triethylenemelamine in the ad-3 region of heterokaryon 12 of Neurospora crassa.
abstract: Studies have been performed to compare the mutagenicity and mutagenic specificity of the trifunctional alkylating agent, triethylenemelamine (TEM), and a closely related monofunctional agent, ethylenimine (EI), in the adenine-3 (ad-3) region of a 2-component heterokaryon (H-12) of Neurospora crassa. The primary objective of our studies was to characterize the genetic damage produced by each agent with regard to (1) mutagenic potency, and (2) the spectrum of specific-locus mutations induced in a lower eukaryotic organism. As in higher eukaryotes, specific-locus mutations in the ad-3 region of H-12 result from gene/point mutations, multilocus deletion mutations, and multiple-locus mutations. Specific-locus mutations resulting from gene/point mutation and multilocus deletion mutation can be detected in higher eukaryotes, but multiple-locus mutations can be detected only with difficulty or not at all. Our experiments with the ad-3 forward-mutation assay have demonstrated that TEM is a strong mutagen (maximum forward-mutation frequency between 100 and 1000 ad-3 mutations per 10(6) survivors) and EI is a moderate mutagen (maximum forward-mutation frequency between 10 and 100 ad-3 mutations per 10(6) survivors) for the induction of specific-locus mutations in the ad-3 region. Classical genetic tests were used to identify the different genotypic classes and subclasses among the EI- and TEM-induced ad-3 mutations from each experiment. The overall data base demonstrates that both EI- and TEM-induced ad-3 mutations result predominantly from gene/point mutations at the ad-3A and ad-3B loci (97.3% and 95.5%, respectively), and infrequently from multilocus deletion mutations (2.7% and 4.5%, respectively). Heterokaryon tests for allelic complementation on TEM- and EI-induced ad-3B mutations, however, have revealed a difference between the percentages showing allelic complementation (63.1% and 40.9%, respectively). Based on the specific revertibility of complementing and noncomplementing ad-3B mutations induced by other agents, this difference in the percentages of ad-3B mutations showing allelic complementation results from a difference between the spectrum of genetic alterations at the molecular level. In addition, comparison of the ratio of TEM-induced ad-3A and ad-3B mutations with those induced by EI has revealed a difference between the ad-3B/ad-3A ratios. Additional comparisons are made of the mutagenic effects of TEM and EI with those of other chemical mutagens and carcinogens in the ad-3 specific-locus assay in Neurospora.
authors.affiliation: Toxicology Branch, National Institute of Environmental Health Sciences, Research Triangle Park, NC 27709-2233, USA.
authors.forename: F J
authors.initials: FJ
authors.lastname: de Serres
authors.forename: H V
authors.initials: HV
authors.lastname: Malling
authors.forename: T M
authors.initials: TM
authors.lastname: Ong
mesh_terms: D000225:Adenine; D001388:Aziridines / Q000737:chemistry / Q000633:toxicity*; D004271:DNA, Fungal / Q000187:drug effects; D005800:Genes, Fungal / Q000187:drug effects; D005804:Genes, Lethal; D005816:Genetic Complementation Test; D008970:Molecular Weight; D016297:Mutagenesis, Site-Directed; D009152:Mutagenicity Tests; D009153:Mutagens / Q000737:chemistry / Q000633:toxicity*; D009492:Neurospora crassa / Q000187:drug effects* / Q000235:genetics; D017354:Point Mutation; D017384:Sequence Deletion; D013329:Structure-Activity Relationship; D014265:Triethylenemelamine / Q000737:chemistry / Q000633:toxicity*
chemical_list: D001388:Aziridines; D004271:DNA, Fungal; D009153:Mutagens; C033132:aziridine; D014265:Triethylenemelamine; D000225:Adenine