DNA-REPLICATION DURING A SERUM-INDUCED S-PHASE IN PRIMATE CV-1 CELLS

We have investigated components of DNA replication in a serum-induced S phase of primate CV-1 cells. Using DNA fiber autoradiography, we found a relative decrease in the frequency of initiation events in mid-S compared with early and late S phase. The other components of DNA replication measured by autoradiography-synchrony of initiation events, size of replication units, incidence of bidirectional replication, and the rate of replication fork movement-remained constant through S phase. When fork movement was measured by density gradient analysis of BUdR- and [3H]-thymidine-substituted DNA, it was also found to remain constant. These results show that most components of DNA replication are invariable through a serum-induced S phase. The changes in initiation frequency support the view that it may be critical in the regulation of ongoing replication. © 1979.