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XB-ART-6058
Mol Biol Cell 2002 Dec 01;1312:4388-400. doi: 10.1091/mbc.e02-07-0449.
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Identification of the nuclear localization signal in Xenopus cyclin E and analysis of its role in replication and mitosis.

Moore JD , Kornbluth S , Hunt T .


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Cyclin-dependent kinase (Cdk)2/cyclin E is imported into nuclei assembled in Xenopus egg extracts by a pathway that requires importin-alpha and -beta. Here, we identify a basic nuclear localization sequence (NLS) in the N-terminus of Xenopus cyclin E. Mutation of the NLS eliminated nuclear accumulation of both cyclin E and Cdk2, and such versions of cyclin E were unable to trigger DNA replication. Addition of a heterologous NLS from SV40 large T antigen restored both nuclear targeting of Cdk2/cyclin E and DNA replication. We present evidence indicating that Cdk2/cyclin E complexes must become highly concentrated within nuclei to support replication and find that cyclin A can trigger replication at much lower intranuclear concentrations. We confirmed that depletion of endogenous cyclin E increases the concentration of cyclin B necessary to promote entry into mitosis. In contrast to its inability to promote DNA replication, cyclin E lacking its NLS was able to cooperate with cyclin B in promoting mitotic entry.

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Species referenced: Xenopus
Genes referenced: ccnb1.2 cdk2

References [+] :
Alt, Phosphorylation-dependent regulation of cyclin D1 nuclear export and cyclin D1-dependent cellular transformation. 2000, Pubmed