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XB-ART-7122
Genes Dev 2002 May 15;1610:1182-94. doi: 10.1101/gad.985302.
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Xic1 degradation in Xenopus egg extracts is coupled to initiation of DNA replication.

You Z , Harvey K , Kong L , Newport J .


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CDK2 activity is regulated by phosphorylation/dephosphorylation, subcellular localization, cyclin levels, and cyclin dependent kinase inhibitors (CKIs). Using Xenopus egg extracts, we find that degradation of Xic1, a Xenopus p21(cip1)/p27(kip1) family member, is coupled to initiation of DNA replication. Xic1 turnover requires the formation of a prereplication complex (pre-RC). Additionally, downstream initiation factors including CDK2, Cdc7, and Cdc45, but not RPA or DNA polymerase alpha, are necessary for activating the degradation system. Xic1 degradation is attenuated following completion of DNA replication. Unlike degradation of p27(kip1) in mammalian cells, CDK2 activity is not directly involved in Xic1 degradation and interactions between Xic1 and CDK2/cyclin E are dispensable for Xic1 turnover. Interestingly, a C-terminal region (162-192) of Xic1 is essential and apparently sufficient for triggering Xic1 ubiquitination prior to degradation. These observations demonstrate that a direct link exists between DNA replication and CKI degradation.

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Species referenced: Xenopus laevis
Genes referenced: cdc45 cdc7 cdk2 cdkn1a cdkn1b cdknx csnk1g2 nsg1 pola1 rpa1 znrd2

References [+] :
Aparicio, Components and dynamics of DNA replication complexes in S. cerevisiae: redistribution of MCM proteins and Cdc45p during S phase. 1997, Pubmed