Cell Cycle Control of DNA Replication by a Homologue from Human Cells of the p34 cdc2 Protein Kinase

Abstract

The regulation of DNA replication during the eukaryotic cell cycle was studied in a system where cell free replication of simian virus 40 (SV40) DNA was used as a model for chromosome replication. A factor, RF-S, was partially purified from human S phase cells based on its ability to activate DNA replication in extracts from G 1 cells. RF-S contained a human homologue of the Schizosaccharomyces pombe p34 cdc2 kinase, and this kinase was necessary for RF-S activity. The limiting step in activation of the p34 kinase at the G 1 to S transition may be its association with a cyclin since addition of cyclin A to a G 1 extract was sufficient to start DNA replication. These observations suggest that the role of p34 cdc2 in controlling the start of DNA synthesis has been conserved in evolution.