INTERFERENCE BY CELLULAR MELANIN WITH ASSAY OF DNA-PROTEIN CROSS-LINKS BY THE POTASSIUM DODECYL-SULFATE PRECIPITATION METHOD

The potassium dodecyl sulfate precipitation method was used to quantif y DNA-protein crosslinks (DPCs) in lysates of melanoma cells exposed t o ultraviolet radiation. Inducing melanin production in these cells be fore exposure to ultraviolet radiation decreased the apparent yield of DPCs. The decrease could also be produced by addition of melanin to l ysates after exposure to crosslinking conditions. Experimental models could attribute this decrease to neither quenching of scintillations f rom the tritium label used nor to an effect of single strand breaks of DNA. This assay appears to be inappropriate for quantification of DPC s in melanized cells.