Transmembrane and ubiquitin-like domain-containing protein 1 (TMUB1), also referred to as hepatocyte odd protein shuttling (HOPS), is a transmembrane ubiquitin-like protein that was originally identified in the regenerated liver. HOPS is a transmembrane protein released into the cell by an enzymatic cleavage. This allows HOPS to be shuttled from the nucleus to the cytoplasm and vice versa, depending on cell cycle and environmental stress conditions. HOPS cDNA expression gives rise to the translation of three different proteins with distinct molecular weights of 27, 24 and 21 kDa, respectively.The three isoforms of HOPS are differentially expressed depending on the tissue being examined. In the brain, the shortest isoform prevails over the other, whereas in the intestine the higher molecular weight isoform prevails among the other two. Indeed, HOPS shows a different concentration of the three isoforms, which can play different cell-dependent functions. The ratio between different isoforms may vary owing to physiopathological changes in the cell (PMID:32860479).16638-1-AP can detect two bands and some literature also detected two bands (PMID:30610893, 29777440, 29967478)