Mutagenesis, Vol. 15, No. 6, 473-477,
November 2000
© 2000 UK Environmental Mutagen Society/Oxford University Press
Oxidative damage and induced mutations in M13mp2 phage DNA exposed to N-nitrosopyrrolidine with UVA radiation
Faculty of Pharmaceutical Sciences, Okayama University, 1-1-1 Tsushima, Okayama 700-8530, Japan and 2 CEA/Département de Recherche Fondamentale sur la Matiere Condensée, SCIB/LAN and UMR, F-38054 Grenoble Cedex 9, France
N-Nitrosopyrrolidine (NPYR) is carcinogenic in rodents and undergoes 
-hydroxylation upon microsomal CYP450 metabolism, giving rise to mutations. Previously, we reported the direct mutagenicity of NPYR, under ultraviolet A (UVA) irradiation, towards Salmonella typhimurium and phage M13mp2. In the present study, we measured the formation of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodGuo) in a replicative form of M13mp2 DNA exposed to NPYR plus UVA. Formation of 5-hydroxy-2'-deoxycytidine in calf thymus DNA treated with NPYR plus UVA was also observed. Singlet oxygen is likely to account for the formation of 8-oxodGuo. We analyzed the spectrum of mutations in lacZ of M13mp2 phages produced on transfecting Escherichia coli with the replicative form of phage DNA that had been treated with NPYR plus UVA. The role of oxidative DNA damage in mutagenesis was explored using mutM-proficient and -deficient E.coli strains as the hosts. A higher level of mutation was observed with the mutM-deficient host than with the -proficient host. Base substitutions at GC pairs predominated in both mutM-proficient and -deficient hosts. With the mutM-deficient host, we observed an overall increase in the percentage of GC
TA transversions. In addition we noted that there were fewer GCAT transitions than in the mutM-proficient host. With these hosts, different hot spots were observed and a new GCTA hot spot was produced. The formation of 8-oxodGuo in DNA, which is known to induce GCTA transversion, may contribute to mutagenesis by NPYR plus UVA.
1 To whom correspondence should be addressed. E-mail: arimoto{at}cc.okayama-u.ac.jp
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