Mutational Specificity of the Ferrous Ion in a supF Gene of Endonuclease III/VIII Deficient Escherichia coli.

When 125 microM Fe2+/EDTA treated plasmid pUB3 was used to transfect an Escherichia coli NKJ2004 (nth nei) host, which is totally defective in glycosylases for thymine glycol and 5-hydroxycytosine, a 3.7 fold increase in mutation frequency was observed. Among 46 supF mutants sequenced, 28 had base substitutions, with G:C-->C:G transversion predominant (14 cases), followed by G:C-->T:A transversion (6 cases) and G:C-->A:T transition (6 cases). The results are consistent with our previous Fe2+ mutagenesis results where, in the wild type host, 78% were base substitutions, with G:C-->C:G transversion (59%) predominant, followed by G:C-->T:A transversion (28%) and G:C-->A:T transition (11%). Treatment of pUB3 DNA with Fe2+/EDTA did not yield formation of Endonuclease III sensitive sites. The possibility of 5-hydroxycytosine as the causative lesion for Fe2+ induced G:C-->C:G transversion is discussed.