DNA REPAIR SYNTHESIS IN MOUSE P‐388 CELLS TREATED WITH MITOMYCIN C

DNA repair synthesis was studied in mitomycin C treated mouse P‐388 cells grown in suspension culture by measuring the incorporation of 3H‐thymidine into non‐replicating DNA. Two methods of density labelling with bromodeoxyuridine were used. By the first method, repair synthesis was measured as incorporation of 3H‐thymidine into light DNA (banding at 1.70 in neutral CsCl) during simultaneous labelling with 3H‐thymidine and bromodeoxyuridine. Increasing amounts of 3H‐labelled light DNA were then found after exposure to increasing concentrations of mitomycin C. By the second method, repair synthesis was measured as incorporation of 3H‐thymidine into hybrid DNA (banding at 1.75 in neutral CsCl) of cells grown in medium containing bromodeoxyuridine prior to treatment with mitomycin C. Exposure to increasing concentrations of the antibiotic then resulted in a progressive accumulation of 3H‐labelled hybrid DNA. The results indicated that the mouse P‐388 cells carried out repair of DNA lesions after treatment with mitomycin C.