Coding properties of a unique apurinic/apyrimidinic site replicated in mammalian cells

The coding properties of abasic sites have been studied in mammalian cells using a single-stranded shuttle vector carrying a unique abasic site. The probe was produced by digestion with the uracil DNA glycosylase of a uracil-containing oligonucleotide which was inserted in the single-stranded vector. After replication in monkey COS7 cells able to support DNA replication of the vector, the plasmid progeny were isolated in bacteria. DNA sequencing of rescued plasmids showed that replication of abasic sites does not lead to preferential insertion of a given base opposite the non-coding site. The four bases were inserted with a frequency which was not statistically different from a random distribution. It appears therefore that the "A rule insertion" opposite a unique abasic site does not apply, at least with the sequence we used, for an exogenous single-stranded DNA replicated in mammalian cells. It was not necessary to induce SOS-like conditions by pretreatment of host cells, in order to replicate abasic sites.