Some aspects of the structure of heat denatured and ultraviolet irradiated DNA

DNA, denatured by heat and rapidly cooled, possesses a structure in which bending occurs at random. The hydrogen bonds between the amine groups of the purine and pyrimidine bases impose a specific secondary structure. The peculiarities of the secondary structure of DNA denatured by heat were studied by means of the reaction with formaldehyde followed by spectrophotometric, immunologic, and enzymologic methods. The utilization of these techniques, together with CsCl density gradient analysis, showed that the uv irradiation of DNA in solution produces an irreversible lesion of the hydrogen bonding, most probably in the internal regions of the DNA molecule, and the formation of formamidic bonds and of thermostable bonds between the two complementary chains of DNA. The separation of this last lesion is catalyzed by the photoreactivator enzyme of baker's yeast. (tr-auth)