DNA BREAKAGE CAUSED BY 334‐nm ULTRAVIOLET LIGHT IS ENHANCED BY NATURALLY OCCURRING NUCLEIC ACID COMPONENTS AND NUCLEOTIDE COENZYMES

The induction of breaks in DNA in vitro caused by 334‐nm UV radíation is enhanced by the following compounds (fluence enhancement factors and concentrations used in parentheses): 4‐thiouridine (6.9, 1 m M ), 5‐methylamino‐2‐thiouridine (7.5, 1 m M ), 2‐thiouracil (41.0, 1 m M ), riboflavin (14.4.0.1 m M ), and the oxidized (6.8, 1 m M ) and reduced (3.4, 1 m M ) forms of nicotinamide adenine dinucleotide. Anoxia and diazobicyclo(2.2.2)octane reduce the number of DNA breaks caused by 334‐nm radiation plus 4‐thiouridine by 70 and 76%, respectively.