Ubiquitin cycles for Golgi fusion

Chains of ubiquitin (Ub) can mark a protein for degradation by the proteasome. Single Ub tags are commonly used as sorting signals for protein trafficking. Now, on page 973, Wang et al. show that Ub also regulates membrane fusion by cycling onto and off of Golgi membranes before and after mitosis.

The Golgi is dismantled during mitosis into membrane fragments; these are reassembled when division is complete. This fusion event requires the p97 AAA-ATPase and its cofactors, p47 and VCIP135. p97 has various other functions, many of which involve Ub, including extracting Ub-tagged ER proteins from the membrane for transport to the proteasome. Ub is also needed during p97-mediated Golgi reassembly, but the authors find that this requirement has nothing to do with protein degradation.

The proteasome was dispensable for Golgi membrane fusion...