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

Abstract

Using a filter binding assay, a protein from human placenta was detected and partially purified, which has a high affinity for N-acetoxy-2-acetylaminofluorene-modified double-stranded DNA (AAF-[3H]DNA) of bacteriophage T7. This protein was 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 h at 4.degree. C, and the extent of binding was proportional to the amount of protein added. Complex formation was dependent on 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 no recognition of single-stranded DNA, double-stranded DNA, supercoiled bacteriophage .vphi.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.