Excision repair in Cockayne syndrome

Cockayne syndrome (CS) is a genetic disorder showing cellular sensitivity to the lethal effects of UV-irradiation. No defects in unscheduled DNA synthesis or in daughter-strand repair have been detected after UV-irradiation of CS cells. We have studied several aspects of excision repair, particularly at early times after UV-irradiation, and with one exception, we have not been able to detect any difference in the response of normal and CS cells to UV-irradiation, by measuring: (1) the rate of formation of incision breaks in the presence of 1-beta-D-arabinofuranosylcytosine (araC); (2) the amount of repair replication as measured by equilibrium centrifugation; (3) the ligation of repaired DNA to pre-existing DNA; (4) the digestibility of repaired DNA after treatment of nuclei with micrococcal nuclease. The single exception was a pair of CS strains from sibling donors in which the rate of uncoupled incision due to the presence of either araC or the specific inhibitor of DNA polymerase alpha, aphidicolin, was slightly faster than in other cells studied. This effect was absent in the heterozygous parents. However, since this was not seen in two other CS strains in the same genetic complementation group, we can not attribute this increased rate of incision to the defective CS gene. We conclude that, within the limits of resolution of these techniques, CS cells do not have a detectable defect in excision repair.