Isolation of nucleolar DNA-binding proteins by simultaneous, competitive DNA--sephadex affinity chromatography.

A new method is described for the isolation of sequence-specific DNA-binding proteins, based on simultaneous, competitive binding to homologous or heterologous DNA. Since both types of DNA are bound to a solid matrix (Sephadex beads), the method may be used for the preparative isolation of proteins which bind preferentially to specific DNA sequences. Fractionation of nucleolar proteins from Novikoff hepatoma ascites cells by this technique yields two protein fractions which show much greater apparent specificity of binding to homologus DNA, in a nitrocellulose filter-binding assay, than unfractionated nucleolar proteins.