This entry contains members of peptidase family C19 known as USP39 (MEROPS identifier C19.972; also known as U4/U6.U5 tri-snRNP-associated protein 2). The name is misleading because the active site residues are not conserved, and members of this cluster are known not to be ubiquitin hydrolases []. Homologues are found in eukaryotes [, ]. It is a component of the spliceosome where it regulates Aurora B mRNA levels, thus playing a role in cytokinesis and in the spindle checkpoint [].