Distinct AAA-ATPase p97 complexes function in discrete steps of nuclear assembly

Although nuclear envelope (NE) assembly is known to require the GTPase Ran, the membrane fusion machinery involved is uncharacterized. NE assembly inv olves formation of a reticular network on chromatin, fusion of this network into a closed NE and subsequent expansion. Here we show that p97, an AAA-A TPase previously implicated in fusion of Golgi and transitional endoplasmic reticulum (ER) membranes together with the adaptor p47, has two discrete f unctions in NE assembly. Formation of a closed NE requires the p97-Ufd1-Npl 4 complex, not previously implicated in membrane fusion. Subsequent NE grow th involves a p97-p47 complex. This study provides the first insights into the molecular mechanisms and specificity of fusion events involved in NE fo rmation.