Quantitation of ultraviolet radiation-induced cyclobutyl pyrimidine dimers in DNA by video and photographic densitometry

Abstract

We have compared video and photographic methods for calculating the number of ultraviolet radiation (uv)-induced pyrimidine dimers in DNA from the bacteriophage T7 exposed to uv (0 to 800 J/m 2) from an FS40 sunlamp. DNA was incubated with a pyrimidine dimerspecific Micrococcus luteus uv endonuclease, subjected to alkaline agarose gel electrophoresis, neutralized, and stained with ethidium bromide, and the DNA fluorescence was recorded either with a video camera or on photographic film. The slopes of the dose-response curves for the number of uv-endonuclease-sensitive sites per 10 3 bases (pyrimidine dimers) was 1.2 (±0.1) × 10 −4 uv-endonuclease-sensitive sites per J/m 2 for the video analysis and 1.3 (±0.04) × 10 −4 uv-endonuclease-sensitive sites per J/m 2 for the photographic analysis. Results for pyrimidine dimer determination by either method were statistically comparable.