Colicin E1 plasmid as a probe for detection and study of anti-dna activity in SLE sera

Tritiated colicin E1 plasmid DNA ([3H]DNA) was purified, characterized and developed as a test antigen for study of anti-DNA antibody activity in a modified Farr assay. The homogeneous molecular weight (4.2 X 10(6) daltons), physical state (intact covalently closed circles), and capacity for intrinsic radioactive labeling to a suitable specific activity were all important properties of the plasmid probe. In addition, the ability of the Farr assay to measure primary antigen/antibody interactions made quantitative determinations of anti-double-stranded DNA (dsDNA) antibody activity possible. Sonication of the plasmid resulted in definable fragments which were thermally denatured and used in the measurement of anti-single-stranded DNA (ssDNA) antibody activity. Results from studies in which unlabeled dsDNA, ssDNA, amd free 2'-deoxyribonucleotides were employed to inhibit binding of [3H]DNA by anti-DNA antibodies indicated the presence of 3 distinct anti-DNA specificities in SLE sera.