Replication kinetics of three DNA sequence families in synchronized mouse cells

Abstract

Balb/C 3T3 cells entered the quiescent G₀ state following serum deprivation. On addition of fresh serum, more than 95% of the culture resumed growth, but with asynchronous kinetics. If hydroxyurea were added just before the first cells reached S phase, at least 90% of the cells accumulated at the Gl/S border over the next ten hours. When the block was removed, the culture moved synchronously into S phase. As the cells traversed S, the replication kinetics of three classes of rapidly renaturing DNA were analyzed. Main band highly repeated DNA and foldback DNA replicated continuously. In contrast, satellite DNA replication did not commence until three hours into S, whereupon its rate of synthesis increased very rapidly, reaching a maximum within the next two hours. These results are discussed in the light of earlier work utilizing other methods of cell synchronization.