Functions Related to Proteasome Proteolysis

The Ubc4/5 sub-family of E2s is much larger in mammals, where it includes 

Ubc7 is localized to the endoplasmic reticulum (ER) through an interaction with a partner protein, Cuel [37], and plays a major role in proteasome degradation. 

So far, Ubc8 has been implicated in the regulated turnover of just one substrate, and its E3 partner(s) remain unknown [57]. Interestingly, the closest mammalian relative of yeast Ubc8 is expressed with a restricted tissue specificity and (in some tissues) in a regulated manner [58, 59]. 

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