Mpr1p, Pad1p N-terminal (MPN) domains without catalytic isopeptidase activity, found in 19S proteasomal subunits Rpn7 and Rpn8
This family includes lid subunits of the 26 S proteasome regulatory particles, Rpn7 (PSMD7; proteasome 26S non-ATPase subunit 7; p44), and Rpn8 (PSMD8; proteasome 26S non-ATPase subunit 8; p40; Mov34). Rpn7 is known to be critical for the integrity of the 26 S proteasome complex by establishing a correct lid structure. It is necessary for the incorporation/anchoring of Rpn3 and Rpn12 to the lid and essential for viability and normal mitosis. Rpn7 and Rpn8 are ATP-independent components of the 19S regulator subunit, and contain the MPN structural motif on its N-terminal region. However, while they show a typical MPN metalloprotease fold, they lack the canonical JAMM motif, and therefore do not show catalytic isopeptidase activity. It is suggested that Rpn7 function is primarily structural.