[Determination of DNA-binding proteins by countercurrent isotachopheresis on nitrocellulose membranes. I. Antibodies to DNA and its adducts].

A very strong electroosmotic counterflow was produced on nitrocellulose membranes during isotachophoresis in a system of 0.06 M Tris-HCl (pH 6.7) as the leading electrolyte and 0.012 M Tris-beta-alanine (pII 8.6) as the terminating one. This counterflow was equal in rate and opposite in direction to the migration of the Cl-/beta-alanine boundary. The rate of counterflow was much higher than the rate of migration of any organic anions, including different proteins. Double-stranded and single-stranded DNA or its adducts were fixed on the nitrocellulose membrane, and the membrane was blocked with unrelated proteins. DNA-binding proteins, namely antibodies to DNA, followed by peroxidase-conjugated anti-IgG, were introduced into the counterflow, which transferred them one after another to the DNA spots. Thus, sequential binding and washing was performed automatically. In this way, antibodies were detected to ds- and ss-DNA, to BrdU-DNA, to Z-DNA, to biotinylated DNA and DNA modified with trans-Pt, as well as development of biotinylated DNA dots by steptavidin-peroxidase.