Proteolysis and DNA Replication: The CDC34 Requirement in the Xenopus Egg Cell Cycle

Abstract

The cell division cycle gene, CDC34 , is required for ubiquitin-mediated degradation of G ₁ regulators and cell cycle progression through the transition from G ₁ to S phase in budding yeast. A CDC34 requirement for S phase onset in higher eukaryotes has not been established. Studies of the simple embryonic cell cycle of Xenopus laevis eggs demonstrated that Cdc34p in a large molecular size complex was required in the initiation of DNA replication. Cdc34p appears to regulate the initiation function of Cdk2–cyclin E, perhaps through the degradation of the Xenopus cdk inhibitor, Xic1.