ABSTRACT
Singlet molecular oxygen is a very reactive species of oxygen which can interact with nucleic acids causing damage to the cell genome. By employing a shuttle vector, which is treated in vitro with chemically generated singlet oxygen, the nature and the consequences of induced DNA lesions have been studied. Breaks in the phosphodiester chain and base modifications specifically at guanine residues are the common lesions observed in treated molecules single-stranded DNA being much more susceptible than double-stranded DNA. These lesions at guanine sites block efficiently DNA polymerase activity in vitro. Vector molecules were introduced into mammalian cells and it was observed that the singlet oxygen induced damages lead to plasmid inactivation (probably due to DNA polymerization blocks) and mutagenesis. The mutations in the supF gene were sequenced and most of them were base substitutions, mainly involving guanines. Thus, the mutagenesis due to singlet oxygen is probably a direct consequence of the processing of guanine damaged bases in mammalian cells.