Abstract

A method has been developed to isolate the photoproducts of ultraviolet-irradiated tobacco mosaic virus ribonucleic acid. The method consists of enzymic hydrolysis of the ultraviolet-irradiated ribonucleic acid and isolation of the photoproducts by paper and ion exchange chromatography. Five photoproducts have been isolated: uridine hydrate, two isomeric forms of cyclobutane-type dimers, and two unknown photoproducts. The amount of uridine hydrate formed is a function of dose and the solvent. The rate of formation of uridine hydrate is greater in water than in deuterium oxide. A deuterium isotope effect of 2.2 was observed. This is in agreement with that observed in the biological inactivation of the viral nucleic acid. The rate of formation of pyrimidine dimers and the two unknown photoproducts is the same whether the irradiation is carried out in water or deuterium oxide. The results suggest that the inactivation of tobacco mosaic virus ribonucleic acid by ultraviolet light is mainly due to pyrimidine hydrate formation in solvents of low ionic strength.

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