Novel DNA replication checkpoint in the assembly of DNA replication complex

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The regulation of the initiation of DNA replication in eukaryotic cells has been studied extensively the last enigmatic question is how cells form pre-initiation complex onto the DNA replication origins. The major factors involved in the assembly of the pre-initiation complex are Sld2-Dpb11,Sld3,GINS (Go, Ichi, Ni, and San), and S-phase kinases (Cdk;cyclin-dependent kinase, and Ddk,;Dbf4-dependent kinase). Recently, Wolter et al. reported that protein phosphatase 2A (PP2A) controls the pre-initiation complex in Xenopus cell-free system (J.Biol.Chem.2002). We have tested whether PP2A controlled the pre-initiation complex in starfish eggs. Neither the catalytic subunit of PP2A ligated with nuclear localization signal peptide sequence was ectopically expressed in starfish eggs nor okadaic acid, potent specific PP2A inhibitor was applied to starfish fertilized eggs, had significant effect to the initiation of the DNA replication.