Ubiquitin and ubiquitinationINTRODUCTIONGeneral understanding of ubiquitin.Ubiquitin is a regulatory protein that plays an important role in the regulation of eukaryotic cells. The word ubiquitin comes from the Latin word ubiquitous, which means everywhere, since this protein is found in all parts of the body. It was first isolated by Goldstein in 1975 from the thymus and was subsequently found in all tissues and organs of eukaryotic cells1. The protein has a molar mass of 8.5 kDa and is composed of 76 amino acids that are highly conserved in all eukaryotic organisms1. There are four genes in the human genome responsible for ubiquitin production including UBB, UBC, UBA52 and RPS27A. Although Ubiquitin is present only in eukaryotes, prokaryotes have a similar protein that performs the same function as ubiquitin, known as ThiS 1. Figure 1 Basic structure of Ubiquitin The structure of Ubiquitin is characterized by an N terminus and a C terminus as a regular protein. Lys 63 and Lys 48 (Figure 1) play an important role in ubiquitination (shown below), the step in post-translational modification in which ubiquitin binds to target proteins. This process is incredibly important as it determines protein function 2. Ubiquitination is the step in post-translational modification in which ubiquitin attaches to target proteins. Ubiquitin plays an important role in post-translational modification, the process that determines the function of a protein. Post-translational modification can be phosphorylation, SUMOlation and ubiquitination 3. Initially ubiquitination was only associated with protein degradation, now ubiquitination has been linked to other cellular functions. There are three enzymes that make ubiquitination possible which include E1 (the enzyme that activates ubiquitin), E2 (ubiquitin conjugating enzyme) and E3 (ubiquitin ligase) 3. This article will be a summary of the structure, function of ubiquitin, the steps of ubiquitination and the application to cancer research.2) Similarities and differences of the Ubiquitin family; StructureThe ubiquitin family is large, but shares some characteristics. Some of these features include; the folding of ubiquitin and the biochemical mechanism they use to bind to the target protein. The structure of ubiquitin was analyzed as part of a larger NMR study to understand new techniques including H/D exchange. This technique has mainly contributed to the information of protein folding.