Repair of depurinated DNA in vitro by enzymes purified from human lymphoblasts.

Alkali-labile lesions introduced into T7 DNA by treatment with methyl methanesulfonate were removed and the DNA was repaired by incubation with DNA polymerase alpha and nuclease from a human lymphoblastoid line followed by the addition of DNA ligase. The nuclease preparation contains both apurinic endonuclease and 5'-3' exonuclease activities. Dinucleotides appear to be the first product of exonuclease action. Repair of methyl methanesulfonate-induced damage can occur by the insertion of only a few nucleotides per lesion as in vivo.