title: Effect of cross-linking on the secondary structure of DNA I. Cross-linking by photodimerization.
abstract: An investigation has been made into the effect produced by photo-induced pyrimidine cross-links upon the secondary structure of DNA. We have studied the effect of uv irradiation upon the B in equilibrium A transition in DNA brought about by a change of solvent from 70 to 80% ethanol. Circular dichroism (CD) was used to monitor the conformational changes. However, we first showed by means of laser Raman spectroscopy that CD is a reliable monitor of the conformational change, even though the DNA is aggregated in 80% alcohol solutions. It is suggested that this aggregation stabilizes the A form through lateral interaction between the helices. The uv irradiation experiments show that pyrimidine-dimer cross-links induced into the B-form DNA will lock it irreversibly into that conformation and prevent it from going to the A form in 80% EtOH solution. The A-form DNA can tolerate a few cross-links but converts cooperatively to the B form if a larger number of cross-links is introduced. Irradiation-induced pyrimidine cross-links create locally denatured regions in B-form DNA. Upon continued irradiation, the entire DNA moelcule becomes denatured.
mesh_terms: D001665:Binding Sites; D002942:Circular Dichroism; D004247:DNA / Q000528:radiation effects; D000431:Ethanol; D007834:Lasers; D046911:Macromolecular Substances; D008970:Molecular Weight; D009690:Nucleic Acid Conformation; D011830:Radiation Effects; D012542:Scattering, Radiation; D013057:Spectrum Analysis; D013950:Thymus Gland; D014466:Ultraviolet Rays
chemical_list: D046911:Macromolecular Substances; D000431:Ethanol; D004247:DNA