A Study of Changes in DNA Conformation Caused by Ionizing and Ultra-violet Radiation by Means of Pulse Polarography and Circular Dichroism

Abstract

Summary The changes in the secondary structure of DNA caused by ionizing and U.V.-radiations were studied by means of circular dichroism and differential pulse polarography. An application of relatively low doses of radiation (of the order of 10⁴ rads or 10⁴ erg mm⁻²) caused an increase of the polarographic reducibility of DNA and an increase of the positive CD band in the vicinity of 275 nm. Doses by one order of magnitude higher brought about a decrease of ellipticity at 275 nm and simultaneously a shift of the pulse-polarographic peak to negative potential values (nearer to the potential of the reduction of the denatured DNA). Irradiation of DNA with low doses of γ-and U.V.-radiation probably induces local changes in angles and distances between the bases in the double helix. No single-stranded fragments are formed. Denatured DNA appeared after irradiating DNA with higher doses of ionizing radiation, or after heating the irradiated samples to a temperature below melting-point.