Initiation of DNA replication in Xenopus egg extracts

In the last decade, extraordinary advances in our understanding of the initiation step of eukaryotic DNA replication have been achieved. Many factors required for replication initiation have been identified, and an elegant model to explain how DNA replication is restricted to a single round per cell cycle has emerged. Of the many experimental approaches used to study DNA replication, egg extracts from Xenopus laevis are among the most powerful, since they recapitulate a complete round of cell-cycle regulated chromosomal DNA replication in vitro. In this review, we discuss current models for how DNA replication is initiated and regulated in Xenopus eggs, and we highlight similarities and differences seen between this and the other most common experimental organisms, yeast and humans.