Separase

Separase is a cysteine protease responsible for triggering anaphase by hydrolysing cohesin which is the protein responsible for binding sister chromatids during metaphase.

When the cell is not dividing, separase is prevented from cleaving cohesin through its association with another protein, securin. On the signal for anaphase, the securin is ubiquitinated and hydrolysed, releasing active separase.

Esp1
Esp1 is a separin protein that cleaves the cohesin subunit Scc1, thus allowing sister chromatids to separate at the onset of anaphase during mitosis. Esp1 is coded by esp1-1 and is regulated by the securin Pds1. During mitosis, sister chromatids comprise the duplicated genetic material of a dividing cell. The two sister chromatids are bound together up until the beginning of anaphase, at which point the mitotic spindle pulls the two sister chromatids apart, leaving each of the two daughter cells with an equivalent number of sister chromatids. The proteins which bind to the two sister chromatids, disallowing any premature sister chromatid separation, are apart of the cohesin protein family. One of these cohesin proteins crucial for sister chromatid cohesion is Scc1. For proper onset of anaphase, the protein Esp1 cleaves Scc1, thus allowing the sister chromatids to separate.

While Esp1 was initially dubbed a separin protein, it is now thought to be a protease, on account of its catalytic function. Because of this, Esp1 is thought to be in the separase family.

The role of Esp1 was discovered by Frank Uhlmann, Friedrick Lottspeich, and Kim Nasmyth in their paper "Sister-chromatids separation at anaphase-onset is promoted by cleavage of the cohesin subunit Scc1" which was published in the July 1999 issue of Nature.