In vivo repair of ENU-induced oxygen alkylation damage by the nucleotide excision repair mechanism in Drosophila melanogaster.
DNA damage caused by oxygen alkylation of bases (mainly at O6-G, O4-T and O2-T positions in DNA) has been correlated with the mutagenic and carcinogenic potency of monofunctional alkylating agents. In all kinds of organisms, repair of O6-alkylG is carried out mainly by the enzyme O6-methyl guanine-DNA methyltransferase (MGMT). However, little is known about the repair of the O-alkylT adducts or about the contribution of nucleotide excision repair (NER) to this process, especially in higher eukaryotes. To study the influence of the NER system on the repair of O-alkylation damage, the molecular mutation spectrum induced by N-ethyl-N-nitrosourea (ENU) in an NER-deficient Drosophila strain, carrying a mutation at the mus201 locus, was obtained and compared with a previously published spectrum for NER-proficient conditions. This comparison reveals a clear increase in the frequency of base pair changes, including GC --> AT and AT --> GC transitions and AT --> TA transversions. In addition, one deletion and two frameshift mutations, not found under NER-proficient conditions, were isolated in the NER-deficient mutant. The results demonstrate that: (1) N-alkylation damage contributes considerably (more than 20%) to the mutagenic activity of ENU under NER-deficient conditions, confirming that the NER system repairs this kind of damage; and (2) that in germ cells of Drosophila in vivo, NER seems to repair O6-ethylguanine and/or O2-ethylcytosine, O4-ethylthymine, and possibly also O2-ethylthymine.
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Departamento de Biología Funcional e Instituto Universitario de Oncología del Principado de Asturias, Universidad de Oviedo, Spain.
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D000477:Alkylating Agents / Q000494:pharmacology; D000478:Alkylation; D000818:Animals; D004249:DNA Damage; D004260:DNA Repair; D029721:Drosophila Proteins; D004331:Drosophila melanogaster / Q000235:genetics*; D005038:Ethylnitrosourea / Q000494:pharmacology; D005136:Eye Proteins; D005260:Female; D019476:Insect Proteins / Q000235:genetics*; D008297:Male; D016296:Mutagenesis; D010100:Oxygen; D014366:Tryptophan Oxygenase
D000477:Alkylating Agents; D029721:Drosophila Proteins; D005136:Eye Proteins; D019476:Insect Proteins; D014366:Tryptophan Oxygenase; C121974:v protein, Drosophila; D005038:Ethylnitrosourea; D010100:Oxygen