A complex of mammalian Ufd1 and Npl4 links the AAA-ATPase, p97, to ubiquitin and nuclear transport pathways

The AAA-ATPase, p97/Cdc48p, has been implicated in many different pathways ranging from membrane fusion to ubiquitin-dependent protein degradation. Binding of the p47 complex directs p97 to act in the post-mitotic fusion of Golgi membranes. We now describe another binding complex comprising mammalian Ufd1 and Np14. Yeast Ufd1p is required for ubiquitin-dependent protein degradation whereas yeast Np14p has been implicated in nuclear transport, In rat liver cytosol, Ufd1 and Np14 form a binary complex, which exists either alone or bound to p97, Ufd1/Np14 competes with p47 for binding to p97 and so inhibits Golgi membrane fusion, This suggests that it is involved in another cellular function catalysed by p97, the most likely being ubiquitin-dependent events during mitosis, The fact that the binding of p47 and Ufd1/Np14 is mutually exclusive suggests that these protein complexes act as adapters, directing a basic p97 activity into different cellular pathways.