Autoradiographic studies of DNA replication in Werner's syndrome cells

We have compared cultured fibroblasts of early passage derived from patients with the Werner syndrome and from normal subjects in several aspects of cell cycle time and DNA replication. The average cycle time was prolonged in Werner's syndrome cells compared with normal cells because of changes in the duration of S phase. The durations of G1 and G2 were unchanged. In addition, the labeling index was lower in Werner's syndrome cells, suggesting that there are two cell-cycle abnormalities in Werner's syndrome cells. The cause of the prolongation of S phase was investigated by DNA fiber autoradiography and alkaline sucrose density gradient sedimentation. The rate of DNA chain elongation was not different in Werner's syndrome cells from that in normal cells, but the frequency of replication initiation was decreased in Werner's syndrome cells.