The HRD4 gene was identical to NPL4, a gene previously implicated in nuclear transport. Using a diverse set of substrates and direct ubiquitination assays, analysis revealed that HRD4/NPL4 is required for a poorly characterized step in ER-associated degradation after ubiquitination of target proteins but before their recognition by the 26S proteasome. This region of the protein contains possibly two zinc binding motifs (Bateman A pers. obs.). Npl4p physically associates with Cdc48p via Ufd1p to form a Cdc48p-Ufd1p-Npl4p complex. The Cdc48-Ufd1-Npl4 complex functions in the recognition of several polyubiquitin-tagged proteins and facilitates their presentation to the 26S proteasome for processive degradation or even more specific processing.