Increased Rate of Repair of Ultraviolet-induced DNA Strand Breaks in Mitogen Stimulated Lymphocytes

Abstract
The rate of repair of strand breaks in UV-irradiated bovine lymphocytes was studied. The extent of breakage of DNA was the same in mitogen-stimulated and unstimulated lymphocytes from 2 breeds of cattle, when determined by sedimentation of nucleoids on sucrose gradients. In mitogen-stimulated cells the time taken to repair DNA strand breaks was 6 h compared to 12 h in stationary phase lymphocytes after a UV dose of 5 J/m2. Apparently, the increased rate of repair of strand breaks is due to the induction of enzymes involved at the post-incision stage of DNA repair. Thus, the increased level of repair synthesis observed in earlier work correlates with an increased rate of repair of DNA strand breaks in phytohemagglutinin-stimulated bovine lymphocytes.