USP39 (ubiquitin specific peptidase 39), also known as SAD1, CGI-21, HSPC332 or SNRNP65, is a 565 amino acid nuclear protein belonging to the peptidase C19 family. Containing one UBP-type zinc finger, USP39 play a role in mRNA splicing and is part of a tri-snRNP complex. USP39 is thought to be required for the stabilization of the spindle checkpoint and may help support successful cytokinesis.