The Protease Activity of Yeast Separase (Esp1) Is Required for Anaphase Spindle Elongation Independently of Its Role In Cleavage of Cohesin

Separase is a caspase-family protease required for the metaphase–anaphase transition in eukaryotes. In budding yeast, the separase ortholog, Esp1, has been shown to cleave a subunit of cohesin, Mcd1 (Scc1), thereby releasing sister chromatids from cohesion and allowing anaphase. However, whether Esp1 has other substrates required for anaphase has been controversial. Whereas it has been reported that cleavage of Mcd1 is sufficient to trigger anaphase in the absence of Esp1 activation, another study using a temperature-sensitive esp1 mutant concluded that depletion of Mcd1 was not sufficient for anaphase in the absence of Esp1 function. Here we revisit the issue and demonstrate that neither depletion of Mcd1 nor ectopic cleavage of Mcd1 by Tev1 protease is sufficient to support anaphase in an esp1 temperature-sensitive mutant. Furthermore, we demonstrate that the catalytic activity of the Esp1 protease is required for this Mcd1-independent anaphase function. These data suggest that another protein, possibly a spindle-associated protein, is cleaved by Esp1 to allow anaphase. Such a function is consistent with the previous observation that Esp1 localizes to the mitotic spindle during anaphase.