Ultraviolet sensitivity of the biological activity of phi-X-174 virus, single-stranded DNA, and RF DNA.

Action spectra for inactivation of varphiX virus, free varphiX single-stranded DNA, and double-stranded varphiX DNA (RF) have been measured using light of wavelength 225-302 mmu. The sensitivity of RF has been determined using bacterial hosts both capable and incapable of reactivation of UV damage. The inactivation of varphiX virus is due, at all wavelengths, to damage to its DNA; it appears that, below 240 mmu, energy absorbed by viral structural protein may inactivate the viral DNA. The variation of the probability of inactivation by an absorbed quantum (quantum yield) with wavelength, in the case of free-single-stranded varphiX DNA, suggests that energy absorbed by pyrimidine residues is more likely to yield inactivation than absorption by purines. This implies that energy transfer is not so extensive as to make all absorbed energy available to pyrimidines.