Repair Synthesis in Human Lymphocytes Provoked by Photolysis of Ethidium Azide

The azide analog of ethidium was mixed with human lymphocytes and when photolyzed with visible light provoked repair synthesis as shown by incorporation of tritiated thymidine in the presence of hydroxyurea. The use of photolyzed drug, or incubation of drug‐cell mixtures in the dark was without effect. These experiments should prove useful in targeting drug action sites and in studying the details of DNA repair.