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Cell Cycle. 2006 Nov 1;5(21):2537-42. Epub 2006 Sep 13.

Nuclear exclusion of separase prevents cohesin cleavage in interphase cells.

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Department of Molecular Biology, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas 75390-9148, USA.


During mitosis, equal transmission of the duplicated chromosomes demands a strict regulation of separase, which cleaves cohesin and triggers sister chromatid separation in anaphase. Vertebrate separase is inhibited by securin and the inhibitory phosphorylation of separase. However, knockout experiments indicate that securin is dispensable and the inhibitory phosphorylation was observed only in M phase cells. This begs the question how cohesin cleavage by separase is prevented in the absence these two mechanisms. Here we show that separase is excluded from cohesin by the nuclear envelope, which forms in telophase and disassembles in mitosis. The exclusion is achieved passively by its large physical mass and may be backed up by the CRM1-dependent nuclear export. A functional NES motif is identified in separase. We demonstrated that the nuclear envelope is sufficient to prevent active separase from cleaving nuclear cohesin. We propose that the nuclear exclusion is important to prevent cohesin cleavage during interphase in the absence of securin and the phosphorylation inhibition.

[Indexed for MEDLINE]

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