P47 IS A COFACTOR FOR P97-MEDIATED MEMBRANE-FUSION

At least two distinct ATPases, NSF and p97, are known to be involved i n the heterotypic fusion of transport vesicles with their target membr anes and the homotypic fusion of membrane compartments(1). The NSF-med iated fusion pathway is the best characterized, many of the components having been identified and their functions analysed(2-7). In contrast , none of the accessory proteins for the p97-mediated fusion pathway h as been identified(8-10). Now we have identified the first such compon ent, a protein of relative molecular mass 47,000 (p47), which forms a tight, stoichiometric complex with cytosolic p97 (one trimer of p47 pe r hexamer of p97). It is essential for the p97-mediated regrowth of Go lgi cisternae from mitotic Golgi fragments, a process restricted to an imal cells(11). As a homologue of p47 exists in budding yeast, this in dicates that it might also be involved in other membrane fusion reacti ons catalysed by p97, such as karyogamy(10).