Fidelity of DNA synthesis in a mammalian in vitro replication system

We have used the simian virus 40 (SV40)-based shuttle vector pZ189 in a forward-mutation assay to determine the fidelity of DNA replication in the in vitro DNA replication system developed by J.J. Li and T.J. Kelly (Proc. Natl. Acad. Sci. USA 81:6973-6977, 1984). We find that very few base substitution errors (approximately 1/180,000 bases incorporated) are made during in vitro replication of the pZ189 vector in a system derived from CV-1 monkey cells. This replication is completely dependent on added SV40 T antigen and presumably reflects synthesis that is initiated at the SV40 replication origin. The observed level of fidelity is far greater than that reported for in vitro replication of DNA by conventionally purified eucaryotic DNA polymerases alpha and beta. Thus, there must be additional cellular factors in the crude in vitro system that serve to enhance the fidelity of DNA replication.