Immunologically active lesions induced on double-stranded DNA with ultraviolet

Some immunochemical properties of double-stranded DNA irradiated with UV were studied, using a radioimmunoassay with irradiated [3H]-DNA and experimentally produced antibodies to DNA. Reactivity of antibodies revealed that irradiated DNA contained an immunologically active structure other than the irradiated DNA specific structure, resembling that of thermally denatured DNA. Inhibition assay demonstrated that while DNA-antibody binding was effectively inhibited by mixed purine and pyrimidine oligonucleotides, thymine dimer containing pyrimidine oligonucleotides derived from the irradiated DNA showed no appreciable inhibition. The antigenic structure specific for irradiated DNA was found to be thermally labile in low salt medium. Cupric and ferrous ions and cysteine added to the DNA solution inhibited antigenicity formation during irradiation, but these substances exhibited no effect on dimer formation in irradiated frozen thymine solution. Calcium ions and histidine were inert for the former reaction but inhibited the latter effectively. This suggested that different mechanisms are involved in the 2 processes. The immunologically active UV-induced lesions appeared to depend mainly on a conformational structure change of the DNA strands rather than on a single modified base moiety. (author)