The NPL4 gene encodes the 608-amino acid, endoplasmic reticulum and nuclear membrane protein Npl4 that forms a complex with p97/Cdc48p and Ufd1p. This complex plays a role in IP3 receptor processing by recognizing ubiquitinated IP3 receptors in the endoplasmic reticulum and delivering them to the proteasome for degradation. The Npl4 protein contains 8 potential N-myristoylation sites, 5 potential N-glycosylation sites, several phosphorylation sites, and a C-terminal zinc finger motif. This protein is 96% homologous to the rat Npl4 protein, 44% homologous to the Caenorhabditis elegans Npl4 protein, and 34% homologous to the Saccharomyces cerevisiae Npl4 protein. Mutations in the NPL4 gene cause defects in nuclear envelope morphology, nuclear protein import, and nuclear poly(A) RNA export.