Ultraviolet-induced DNA excision repair in human B and T lymphocytes. II. Effect of inhibitors and DNA precursors.

Despite their great sensitivity to ultraviolet light purified human B and T lymphocytes are capable of complete repair provided that the ultraviolet dose does not exceed 0.5 Jm-2. Their capacity to repair, as measured by the restoration of DNA supercoiling in preparations of nucleoids, and their survival are significantly increased in the presence of deoxyribonucleosides. Certain agents which inhibit semi-conservative DNA synthesis (hydroxyurea, 1-beta-D-arabinofuranosylcytosine (arafCyt) either stop or delay the repair process in lymphocytes. The effect of hydroxyurea is eventually overcome spontaneously, but changes in the sedimentation behaviour of ultraviolet-irradiated nucleoids caused by arafCyt can only be neutralized by addition of deoxycytidine. The effective inhibition of repair by arafCyt permits the detection of extremely small amounts of ultraviolet damage and also the estimation of when repair is complete.