Xeroderma pigmentosum: in vitro complementation of DNA repair endonuclease

The DNA repair endonuclease activity has been studied in several xeroderma pigmentosum (XP) cell lines of complementation groups A and C. phi X174 RFI DNA treated with u.v.-light or OsO4 was used as a substrate. All XP cells tested appeared to lack this enzyme compared to control cells. However, when extracts from complementation groups A and C were mixed, activity levels close to that of the control cells were found, clearly indicating that the two cell lines can complement each other with regard to the DNA repair endonuclease activity. The XP cells were found to contain normal levels of AP-endonuclease.