Inactivation of Bacteriophage Lambda by Near–ultraviolet Irradiation in the Presence of Chlorpromazine

Bacteriophage λvir was inactivated when it was irradiated with near‐UV light in the presence of chlorpromazine. DNA strand breakage in the treated phage was indicated by alkaline sucrose gradient centrifugation. The number of the breaks was increased with increasing fluence. Although the inactivation rate was enhanced with a decreasing salt concentration in the reaction mixture and under a nitrogen atmosphere, the number of the strand breaks was not altered in either case. Therefore, the DNA strand breakage is not a sole lethal damage in the treated phage. The addition of NaN3 repressed the inactivation and the reaction in a D2O medium enhanced the inactivation even if the reaction mixture was irradiated under anaerobic conditions. Under anaerobic conditions, the inactivation occurs presumably via a radical mechanism.