Influence of RNA synthesis on DNA-repair replication in human cell extracts

An in vitro system allowing human cell extracts to carry out excision repair in ultraviolet light-irradiated, closed circular DNA was used to study the influence of transcription on repair synthesis. RNA synthesis from plasmid DNA containing bacterial transcription units was obtained by addition of Escherichia coli RNA polymerase and ribonucleoside triphosphates to the repair-incubation mixture. No increase in UV-stimulated repair replication was observed under transcriptional conditions; in fact, an inhibition of repair replication occurred, possibly due to impairment of DNA polymerization. This is unlike the in vivo situation where preferential DNA repair of transcribed genes has been found after UV-irradiation. Possible factors important for preferential repair of expressed genes in mammalian cells are discussed.