ACTIVATION OF THE PROTEASOME DURING XENOPUS EGG ACTIVATION IMPLIES A LINK BETWEEN PROTEASOME ACTIVATION AND INTRACELLULAR CALCIUM-RELEASE

Ubiquitin-dependent proteolysis is required for cell cycle progression . Here, we demonstrate that the proteasome is activated during in vivo Xenopus egg activation, induced by treatment with the calcium ionopho re A23187. It was found that activation is due to the calcium-induced assembly of the 26 S proteasome from the 20 S proteasome. We propose t hat proteasome activation is regulated by cell cycle calcium transient s, which are controlled upstream by an endogenous cell cycle oscillato r that is independent of the cyclin-dependent kinase cycle. (C) 1996 A cademic Press, Inc.