The following article requires a subscription:



(Format: HTML)

ALTHOUGH mitotic cyclins are well-known substrates for ubiquitin-mediated proteolysis at the metaphase-anaphase transition [1-4], their degradation is not essential for separation of sister chromatids [5-8]; several lines of evidence suggest that proteolysis of other protein(s) is required, however [4,6,9-11]. Here we report the anaphase-specific proteolysis of the Schizosaccharomyces pombe Cut2 protein, which is essential for sister-chromatid separation [12,13]. Cut2 is located in the nucleus, where it is concentrated along the short metaphase spindle. The rapid degradation of Cut2 at anaphase requires its amino-terminal region and the activity of Cut9 ( [14]), a component of the 20S cyclosome/anaphase-promoting complex (APC), which is necessary for cyclin destruction [3,4,11]. Expression of non-degradable Cut2 blocks sister-chromatid separation but not cell-cycle progression. This defect can be overcome by grafting the N terminus of cyclin B onto the truncated Cut2, demonstrating that the regulated proteolysis of Cut2 is essential for sister-chromatid separation.

(C) 1996 Macmillan Magazines Ltd.