The Involvement of cdc2 in Cell Cycle Control of DNA Replication in Xenopus Egg Extracts

Abstract

DNA replication must be strictly controlled in order to coordinate it with the other major events of the cell division cycle. Two main strategies could be employed to investigate this problem. The first is to generate temperature-sensitive (cdc) mutations in yeast that are specifically defective in steps that normally control chromosomal DNA replication. Although this approach has identified a range of genes that are required for DNA replication, the absence of cell-free systems from yeast means that the precise function of these gene products often remains unknown. The second approach is to study cell-free systems that are capable of supporting the initiation of DNA replication from chromosomal (non-viral) origins of replication under cell cycle control. This has been possible following the development of a cell-free extract of Xenopus eggs (Lohka and Masui, 1983) that can support the efficient initiation and completion of chromosomal DNA replication in vitro (Blow and Laskey, 1986; Blow and Watson, 1987). However, the dependence of chromosome replication on a range of basic cellular functions, such as nuclear assembly, severely complicates biochemical fractionation of replication proteins from this system.