This is the most conserved part of the core region of Ufd2P ubiquitin elongating factor or E4, 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, pfam04564, which has ligase activity.