Mutation spectrum resulting in M13mp2 phage DNA exposed to N-nitrosoproline with UVA irradiation

•Mutation frequency on M13mp2 DNA increased after exposure to NPRO + UVA.•Single-base substitutions, especially GC to CG transversions increased.•Non-clustering of the GC to CG mutations suggests NPRO + UVA damage to DNA is random.

N-nitrosoproline (NPRO) is endogenously formed from proline and nitrite. In an effort to delineate the mechanism of NPRO-induced photomutagenicity, we investigated the mutagenic spectrum of NPRO on M13mp2 DNA with UVA irradiation. Following exposure to NPRO and UVA, the mutation frequency increased significantly in an NPRO and UVA dose-dependent manner. The sequence data derived from seventy of the mutants indicated that mutagenesis resulted mainly from an increase in single-base substitutions, the most frequent being GC to CG transversions. Non-clustering of the GC to CG mutations suggests that NPRO + UVA damage to DNA is random. These transversions may be caused by guanine adducts in DNA or in part by oxidatively modified guanine in DNA exposed to NPRO and UVA.