UC Riverside

Genome integrity is constantly challenged by endogenous or exogenous genotoxic agents, which can give rise to various DNA adducts. After metabolic activation, tobacco-specific nitrosamines N-nitrosonornicotine (NNN) and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) can lead to pyridyloxobutylphosphotriesters (POB-PTEs) in DNA. Here, we synthesized oligodeoxyribonucleotides containing a site-specifically inserted SP- or RP-POB-PTE flanked by two thymidines, and we examined the impact that these lesions have on DNA replication in Escherichia coli cells. We found that these two lesions are not strong impediments to DNA replication, and their replicative bypass is not modulated by genetic depletion of the three SOS-induced DNA polymerases or Ada protein. In addition, neither SP- nor RP-POB-PTEs was mutagenic in E. coli cells. Together, our study unveiled, for the first time, the influence of tobacco-specific nitrosamine-induced POB-PTE lesions on DNA replication in vivo.