ABSTRACT
We have studied the specificity of singlet oxygen (1O2) mutagenesis in single-stranded DNA phage by analysing 1O2-induced mutations in the lac insert of the M13 mp 19 hybrid phage. 107 lac mutants were analysed showing mainly single-base substitutions with a total of 93% and 7% of 40-50 base deletion mutations. Most of the substitutions are G----T and C----A transversions with respectively 27 and 54% of the mutations. The replicative form of the M13 mp 19 DNA (RFDNA) was used as substrate for the 1O2 reactions, there are then two types of progeny phages DNA's. As guanine residues are the targets of the oxidation, it appears that both types of transversions are provided by one type of lesion: the guanine oxidised by 1O2 is read like a thymine by E. coli DNA polymerase-I.
