Characterization of DNA-protein complexes induced in intact cells by the carcinogen chromate

Potassium chromate induced the formation of DNA-protein complexes in cultured Chinese hamster ovary cells. The DNA-protein complexes were isolated by ultracentrifugal sedimentation in the presence of 2% sodium dodecyl sulfate (SDS) and 5 M urea. Two-dimensional SDS-polyacrylamide gel electrophoresis analysis of the chromate-induced DNA-protein complexes revealed that two acidic proteins of 53 and 45 kDa and a basic protein of 54 kDa were selectively complexed to the DNA. Numerous other proteins also became associated with the DNA to a lesser degree as the chromate concentration was increased. Nuclease digestion was not a prerequisite for the resolution of the protein component of the DNA-protein complexes using two-dimensional gel electrophoresis. Ultracentrifugal analysis of the DNA-protein complexes in the presence of proteinase K, nucleases, or a chelating agent demonstrated that protein aggregation was not responsible for the increased protein recovery in chromate-treated samples and that the complexes were disrupted by EDTA. These data suggest that the selectively complexed proteins were associated with the DNA through strong interactions that may be mediated by the trivalent form of chromium.