Recognition of chemical carcinogen-modified DNA by a DNA-binding protein

Using filter binding assay, we have detected and partially purified a protein from human placenta that has a high affinity for N-acetoxy-2-acetylaminofluorene-modified double-stranded DNA(AAF)-[³H]DNA) of bacteriophage T7. This protein has been partially purified from a 1 M NaCl extract of a crude nuclear fraction by a combination of ion-exchange and nucleic acid affinity chromatography. With AAF-[³H]DNA as the substrate, the binding reaction reached equilibrium within 1 hr at 4°C, and the extent of binding was proportional to the amount of protein added. Complex formation was dependent on both pH and salt concentration and was unaffected by the presence of sulfhydryl-blocking agents. The purest protein fraction also recognizes DNA modified with methylmethanesulfonate or methylnitrosourea. It shows, little or nor recognition of single-stranded DNA, double-stranded DNA, supercoiled bacteriophage ∅X174 DNA, partially depurinated DNA, glucosylated bacteriophage T4 DNA, or UV-irradiated DNA. No endo- or exonuclease activity, DNA polymerase activity, or glycosylase activity for AAF-DNA was detectable in the preparation.