Cells synchronized in S phase show increased rate of repair of UV damaged plasmids.

The capacity for nucleotide excision repair of cells synchronized in S phase and unsynchronized cells was compared by the host cell reactivation assay and the cell-free repair system. HeLa cells were transfected with in vitro damaged by UV irradiation pEGFP and the repair capacity was determined by the number of fluorescent cells. In the cell-free repair system, the repair capacity of protein extracts isolated from K562 cells was determined by measuring the transformation efficiency of UV irradiated pBlueScript incubated in the extracts. In both cases, the repair capacity of the cells synchronized in S phase cells was 30-50% higher than the repair capacity of unsynchronized cells.