Identification of the nuclear localization signal in Xenopus cyclin E and analysis of its role in replication and mitosis.
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.[1]References
- Identification of the nuclear localization signal in Xenopus cyclin E and analysis of its role in replication and mitosis. Moore, J.D., Kornbluth, S., Hunt, T. Mol. Biol. Cell (2002) [Pubmed]
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