InterPro domain: IPR019474

This entry represents the most conserved part of the core region of ubiquitin conjugation factor E4 (or Ub elongating factor, or Ufd2P), running from helix alpha-11 to alpha-38. It consists of 31 helices of variable length connected by loops of variable size forming a compact unit; the helical packing pattern of the compact unit consists of five structural repeats that resemble tandem Armadillo (ARM) repeats. This domain is involved in ubiquitination as it binds Cdc48p and escorts ubiquitinated proteins from Cdc48p to the proteasome for degradation. The core is structurally similar to the nuclear transporter protein importin-alpha. The core is associated with the U-box at the C terminus, ( IPR003613 ), which has ligase activity.

Ubiquitin conjugation factor E4 is involved in N-terminal ubiquitin fusion degradation proteolytic pathway (UFD pathway). E4 binds to the ubiquitin moieties of preformed conjugates and catalyses ubiquitin chain assembly in conjunction with E1, E2, and E3. E4 appears to influence the formation and topology of the multi-Ub chain as it enhances ubiquitination at 'Lys-48' but not at 'Lys-29' of the N-terminal Ub moiety.