Aphidicolin and 1-beta-D-arabinofuranosylcytosine strongly inhibit transcriptionally active DNA repair in normal human fibroblasts.

Both aphidicolin and 1-beta-D-arabinofuranosylcytosine (araC) inactivate DNA polymerases alpha, delta and epsilon, and according block long-patch excision repair in mammalian cells. We report here that in normal human fibroblasts both compounds strongly inhibit the repair of damage induced by UV or 4-nitroquinoline-1-oxide in the transcriptionally active c-myc gene, as indicated by the appearance of DNA strand breaks in carcinogen-treated cultures that were subsequently incubated in the presence of either polymerase inhibitor. We further demonstrate that the repair of UV photoproducts in the c-myc gene can be monitored by photolysis (313 nm) of DNA repaired in the presence of bromodeoxyuridine (BrdUrd). In UV-irradiated cultures, the incidence of aphidicolin- or araC-accumulated strand breaks was approximately 70% of that detected by the BrdUrd photolysis assay. Our data therefore implicate a critical role for DNA polymerases alpha, delta and/or epsilon in gene-specific repair in human cells. The techniques described here may prove useful in the study of DNA repair in defined sequences of the human genome following exposure to a diverse array of physical and chemical genotoxic agents.