Changes in DNA supercoiling during repair of gamma-radiation-induced damage.

Enriched human B-lymphocyte and T-lymphocyte subpopulations were isolated by means of two Percoll density gradient centrifugation steps. Strand-break repair kinetics of 60Co gamma-irradiation-damaged DNA were obtained by applying a modified nucleoid sedimentation technique. Although no variations in the strand-break repair patterns of B-cells and T-cells within an individual could be detected, variations between individuals were evident. Changes in DNA supercoiling during the repair process were studied by means of ethidium bromide intercalation. The supercoiled conformation of DNA in peripheral lymphocyte subpopulations displayed similar undulating patterns within an individual, variations occurring between individuals. The results of this study indicate that alterations to the higher-order structure (supercoiling) of DNA are integral to the repair process.