CDK Phosphorylation of a Novel NLS-NES Module Distributed between Two Subunits of the Mcm2-7 Complex Prevents Chromosomal RereplicationD

• Published in: Molecular biology of the cell Vol. 16; no. 10; pp. 5026 - 5039
• Main Authors: Liku, Muluye E., Nguyen, Van Q., Rosales, Audrey W., Irie, Kaoru, Li, Joachim J.
• Format: Journal Article
• Language: English
• Published: The American Society for Cell Biology 01-10-2005
• ISSN: 1059-1524
• DOI: 10.1091/mbc.E05-05-0412

Cyclin-dependent kinases (CDKs) use multiple mechanisms to block reassembly of prereplicative complexes (pre-RCs) at replication origins to prevent inappropriate rereplication. In
Saccharomyces cerevisiae
, one of these mechanisms promotes the net nuclear export of a pre-RC component, the Mcm2-7 complex, during S, G2, and M phases. Here we identify two partial nuclear localization signals (NLSs) on Mcm2 and Mcm3 that are each necessary, but not sufficient, for nuclear localization of the Mcm2-7 complex. When brought together in
cis
, however, the two partial signals constitute a potent NLS, sufficient for robust nuclear localization when fused to an otherwise cytoplasmic protein. We also identify a Crm1-dependent nuclear export signal (NES) adjacent to the Mcm3 NLS. Remarkably, the Mcm2-Mcm3 NLS and the Mcm3 NES are sufficient to form a transport module that recapitulates the cell cycle-regulated localization of the entire Mcm2-7 complex. Moreover, we show that CDK regulation promotes net export by phosphorylation of the Mcm3 portion of this module and that nuclear export of the Mcm2-7 complex is sufficient to disrupt replication initiation. We speculate that the distribution of partial transport signals among distinct subunits of a complex may enhance the specificity of protein localization and raises the possibility that previously undetected distributed transport signals are used by other multiprotein complexes.