XPG ENDONUCLEASE MAKES THE 3' INCISION IN HUMAN DNA NUCLEOTIDE EXCISION-REPAIR

HUMANS With a defect in the XPG protein suffer from xeroderma pigmento sum (XP) resulting from an inability to perform DNA nucleotide excisio n repair properly(1-4). Here we show that XPG makes a structure-specif ic endonucleolytic incision in a synthetic DNA substrate containing a duplex region and single-stranded arms. One strand of the duplex is cl eaved at the border with single-stranded DNA. A cut with the same pola rity is also made in a bubble structure, at the 3' side of the central ly unpaired region. Normal cell extracts introduce a nick 3' to a plat inum-DNA lesion, but an XP-G cell extract is defective in making this incision. These data show that XPG has a direct role in making one of the incisions required to excise a damaged oligonucleotide, by cleavin g 3' to DNA damage during nucleotide excision repair.