Background：

UBTD2 (ubiquitin domain containing 2)， also known as DCUBP， DC-UbP or SB72， is a 234 amino acid cytoplasmic and mitochondrial ubiquitin-like (UbL) protein that contains one C-terminal UbL domain. UbL proteins are involved in a variety of cellular processes， including DNA repair， protein sorting， apoptosis， protein degradation， cell division and autophagy. Predominantly expressed in dendritic cells and detected at high levels in tumor cell lines， UBTD2 has been implicated in apoptosis， cellular differentiation and tumorigenesis. The UbL domain of UBTD2 is 55% similar and 28.6% identical to the amino acid sequence of ubiquitin， but it lacks the Gly-Gly motif that is essential for ubiquitination. As its UbL domain does not actively ubiquitinate proteins， UBTD2 is believed to function as a shuttle factor involved in the ubiquitin system.