Mutagenesis resulting from depurination is an SOS process.

When bacteriophage phi X174 am3 DNA depurinated in vitro is transfected into E. coli spheroplasts prepared from bacteria previously exposed to UV light, a strong mutagenic response is observed. This mutagenic response does not occur in spheroplasts derived from pre-irradiated bacteria carrying defective recA, recF or umuC genes. These findings indicate that mutagenesis at apurinic sites is an SOS-dependent process. The mutagenic response is not dependent on the multiplicity of transfection. This suggests that mutagenesis is not mediated by recombination.