Jab_MPN domain binds directly to ubiquitin with an affinity comparable to other known UBDs, Proteins with this domain include proteasome regulatory subunits, eukaryotic initiation factor 3 (eIF3) subunits and regulators of transcription factors. They are metalloenzymes that function as the ubiquitin isopeptidase/ deubiquitinase in the ubiquitin-based signaling and protein turnover pathways in eukaryotes (1).

1. Verma R , Aravind L , Oania R , McDonald WH , Yates JR 3rd , Koonin EV , Deshaies RJ(2002). Role of Rpn11 metalloprotease in deubiquitination and degradation by the 26S proteasome. Science., 298(5593):611-5. PMID:12183636