Replicative DNA synthesis has been measured throughout the S phase in
synchronized populations of Chinese hamster ovary cells, When exponent
ially growing, cells in suspension cultures were subjected to counterf
low centrifugal elutriation and the resolution power was increased the
biphasic replication profile has been resolved and multiple subphases
were distinguished, These replication peaks, termed replication check
points, are distributed evenly throughout the S phase, The replication
checkpoints have been characterized by their average C values corresp
onding to 2.05, 2.12, 2.2, 2.45, 2.6, 2.8, 2.95, 3.15, 3.3, 3.45, and
3.85.