Action spectrum for inactivation by ultraviolet light of bacteriophage T4 substituted with 5-bromodeoxyuridine

Abstract

5-Bromodeoxyuridine-substituted T4 phage was found to be about 4–5 times more sensitive to inactivation by ultraviolet light than unsubstituted T4 in the wavelength range between 235 and 289 mμ; above 289 mμ the relative sensitivity increased very rapidly to a maximum of 500–1000 near 313 mμ before decreasing again at about 334 mμ. No significant increase in sensitivity was noted at 365 or 404 mμ. The results imply that 5-bromodeoxyuridine nucleotides are involved in the primary steps of the photochemical inactivating reactions and that there is no electronic transition of 5-bromodeoxyuridine in the 300–334 mμ region capable of causing inactivation comparable to that due to the 280 mμ pi to pi∗ transition; they are compatible with the hypothesis of exciton travel. The action spectrum of T6 bacteriophage was also determined.