Misincorporation rate and type on the leading and lagging strands of UV-damaged DNA.

We have examined the fidelity of replication of the leading and lagging strands of UV-irradiated DNA by using an EBV-derived shuttle vector system which contains as marker gene for mutation analysis the bacterial gpt gene in both orientations relative to the EBV oriP. Human cells stably transformed with this vector were UV irradiated and gpt mutation rate and type were analysed. An increased mutagenicity associated with UV irradiation was observed, but the average error frequency was unaffected by the direction of replication of the target gene. Some variability by position and sequence context of leading and lagging strand errors was detected, suggesting that the different architecture of the replication complex for the two strands might, to some extent, affect mutation spectra. The comparable fidelity of translesion replication on the leading and lagging strands is in agreement with the current model for eukaryotic replication that postulates the simultaneous synthesis of both strands by a DNA polymerase with a proof-reading exonuclease.