Miscoding and misincorporation of 8-oxo-guanine during leading and laggingstrand synthesis in Escherichia coli

We examined whether strand identity with respect to DNA replication influen ces strand bias for 8-oxo-7,8-dihydroguanine (8-oxoG) mutagenesis. The spec ificity of 8-oxoG mutagenesis was determined in a mutM mutY or a mutT strai n carrying the supF gene on one of two vectors that differed only in the or ientation of supF with respect to a unique origin of replication. Most of t he supF mutations in the mutM mutY strain were base substitutions (67%), pr edominantly G:C --> T:A transversions (>64%), while the majority in the mut T strain were base substitutions (>92%), predominantly A:T --> C:G transver sions (>91%). The distributions of frequently mutated sites of G:C --> T:A and A:T --> C:G transversions in the supF gene in the mutM mutY and mutT st rains, respectively, did not differ markedly between the two vectors. These results suggest that gene orientation is not an important determinant of t he strand bias of 8-oxoG mutagenesis.