Induced mutations in M13mp2 phage DNA exposed to N-nitrosopyrrolidine withUVA irradiation

It is known that N-nitrosopyrrolidine (NPYR), a carcinogen in rodents, is m etabolically activated by microsomal cytochrome P450 to form an alpha-hydro xylated derivative, which induces mutations. The mutations have been demons trated by use of Salmonella typhimurium and Escherichia coli. We discovered directly acting mutagenicity of NPYR plus ultraviolet light-A (UVA) in bac teria and phage. with an O-6-alkyltransferase-deficient strain of S. typhim urium, the NPYR plus UVA treatment gave greater mutation Frequencies compar ed to those found with the parent strain. We identified the structure of th e direct-acting mutagen as N-nitroso-1-phosphonooxypyrrolidine, and analyze d the spectrum of mutations induced in the DNA of M13mp2 phage. The basepai r substitutions GC to TA and GC to AT appear to occur predominantly. Severa l hotspots were observed. In the conditions where SOS response was induced in the host E. coil, greater varieties of mutations were observed in phage DNA compared to those without the SOS response induction. These results sug gest that alkylations of DNA occur by the photoactivated NPYR. The roles of the produced damage to the mutations are discussed. Environ. Mol. Mutagen. 34:24-29, 1999. (C) 1999 Wiley-Liss, Inc.