Cdc48pNpl4p/Ufd1p binds and segregates heterodimeric membrane anchored/tethered transcription factor complexes via a poly-ubiquitin signal present on the anchors in vitro

摘要

Cdc48p is an abundant and conserved member of the AAA ATPase family of molecular chaperones. Cdc48p performs ubiquitin selective functions, which are mediated by numerous ubiquitin-binding adaptors, including the Npl4p-Ufd1p complex. Previous studies suggest that Cdc48p-containing complexes carry-out many biochemical activities, including ubiquitination, deubiquitination, protein complex segregation and targeting of ubiquitinated substrates to the proteasome. The molecular mechanisms by which Cdc48p containing complexes participate in these processes remain poorly defined. We show here using physiologically relevant Cdc48p substrates (i.e. endoplasmic membrane associated/tethered dimers of Mga2p and Spt23p) and in vitro systems with purified proteins that Cdc48p^Npl4p/Ufd1p binds to and promotes segregation of the tethered proteins via a poly-ubiquitin signal present on the membrane-bound proteins. Mobilization does not involve retrotranslocation of the associated anchors. These results provide biochemical evidence that Cdc48p^Npl4p/Ufd1p functions as a poly-ubiquitin-selective segregase and that a poly-ubiquitin-Cdc48p-pathway modulates protein interactions at cell membranes.