Antibodies to Z-DNA interact with form V DNA

Abstract

Annealing of single-stranded (ss) DNA rings of complementary base sequence gives rise to the so-called form V DNA which is characterized by a linking number of zero¹. The similarity of the circular dichroism spectrum of form V DNA¹ with that of the 1:1 mixture of the low salt (B-type) and the high salt (Z-type) form of poly(dG-dC) ⋅ poly(dG-dC)^2,3 suggests that form V DNA might contain left-handed double-helical DNA of the Z-type. The discovery that the left-handed Z-form of poly(dG-dC) ṁ poly(dG-dC) induces a strong immune response^4,5 has provided a novel means of searching for DNA of this particular conformation⁶. We therefore used antisera and monoclonal antibodies to Z-DNA to determine whether form V DNA contains stretches of left-handed double-helical conformation. We report here that form V DNA competes in the binding of antibodies to Z-form poly(dG-dC) · poly(dG-dC). The competition by form V DNA is similar to that of (dG-dC)₅·(dG-dC)₅. Thus, DNA of natural base sequence, when forced to adopt left-handed conformations by topological restrictions, is recognized by antibodies against Z-DNA