Human Leukocyte Antigen-F Associated Transcript 10 (FAT10), also known as Ubiquitin D (UBD), is a 165 amino acid (aa) member of the Ubiquitin-like family of proteins. Human FAT10 has a predicted molecular weight of 18.5 kDa and shares 69% aa sequence identity with mouse FAT10. Human FAT10 mRNA is expressed as a single transcript in lymphoblastoid lines and dendritic cells, but more than one mRNA transcript has been identified for murine FAT10. FAT10 can also be induced by IFN-gamma and TNF-alpha in some cell lines. Structurally, FAT10 consists of two Ubiquitin-like domains that are connected by a short linker. Like Ubiquitin, FAT10 has a C-terminal glycine residue that can be used to form isopeptide bonds with target proteins. FAT10-conjugated proteins are targeted to the proteasome where the 26S Proteasome subunit S5a/Angiocidin binds to FAT10 and enables subsequent degradation of the conjugated protein. In addition to S5a/Angiocidin, FAT10 has been shown to interact with Huntingtin, Ataxin-1, MAD2, and NUB1L. FAT10 has been implicated in a number of biological processes such as cell cycle control, antigen presentation, and cytokine response.