Base excision repair of DNA in γ-irradiated human cells

Abstract

Escherichia coli endonuclease IV was used to incise cellular DNA specifically at apurinic/apyrimidinic (AP) sites prior to alkaline elution to measure the resulting DNA strand breaks. .gamma.-Irradiated HeLa cells initially contained DNA strand breaks and no AP sites. Upon incubation at 37.degree. C the strand breaks were rapidly repaired and AP sites were generated and subsequently repaired. The transient nature of the AP sites indicates the in vivo operation of a base excision repair pathway whereby damaged bases are removed from DNA by DNA glycolases to produce AP intermediates that are then substrates for AP endonucleases.