INACTIVATION OF A RHIZOBIUM BACTERIO-PHAGE BY ULTRAVIOLET RADIATION OF DIFFERENT WAVE-LENGTHS

Abstract— The action spectrum for inactivation of a Rhizobiurn bacteriophage by U.V. radiation follows the shape of the absorption spectrum of DNA between the wave-lengths of 240 and 290 mμ (where inactivation probably reflects damage to the nucleic acid only), and deviates sharply upwards at wave-lengths shorter than 240 mμ (where inactivation may depend on damage to both the nucleic acid, and protein of the phage). The rate of inactivation follows first order kinetics approximately at all wave-lengths tested. Infectivity of the phage is halved when each mg of the phage nucleic acid has absorbed about 0 08 J of radiation energy at any wave-length between 240 and 290 mμ.
The bacteriopharge can be photoreactivated after inactivation at any wave-length between 230 and 290 mμ, but less so after inactivation at 230 mμ than at any wave-length above 240 mμ. No evidence was found to suggest that dimerization of thymine residues of the phage-DNA plays any part in the mechanism of inactivation of the bacteriophage by U.V. radiation.