Depurination causes mutations in SOS-induced cells.

Abstract

Introduction of apurinic sites into .vphi.X174 am3 DNA leads to loss of biological activity when measured in a transfection assay. For single-stranded DNA, approximately one apurinic site constitutes a lethal hit; for double-stranded (RFI) DNA, approximately 3.5 hits/strand are lethal. When the reversion frequency of am3 DNA is measured, no increase due to depurination is observed above the background level. A large increase in reversion frequency is observed when the same DNA is assayed by using spheroplasts derived from bacteria (Escherichia coli) previously exposed to UV light. Apurinic sites are evidently impediments to a replicating DNA polymerase; however, nucleotides can be incorporated opposite these sites under SOS-induced conditions. The frequency of mutagenesis per apurinic site may be < 1 in 1400 in normal spheroplasts, and 1 in 100 in SOS-induced spheroplasts. [Applicability to chemical carcinogenesis is discussed.].