The ultraviolet light inactivation of phi-X174 bacteriophage at different wave lengths and pH's.

The bacterial virus, PhiX174, which contains a single strand of DNA has been inactivated by different wave lengths of monochromatic ultraviolet light at pH 7, 2, and 12. The action spectra for inactivation at these three pH's all showed minima at 2400 A rather than at 2300 A, which is the characteristic absorption minimum of DNA. The shapes of the action spectra have been analyzed in terms of the effects of absorbed light on the pyrimidines and purines rather than the effect on nucleoprotein. In this interpretation the pyrimidines are at least 2 to 3 times more sensitive than the purines. The quantum yield for inactivation of the virus at 2650 A and pH 7 is 0.006. The quantum efficiency for quanta absorbed in the pyrimidines is 0.0085 and for the purines 0.0035. It is pointed out that action spectra for single- and double-stranded polynucleotides should have minima at different wave lengths, and that this difference may be used to distinguish between these two configurations in vivo.