UBA5 (ubiquitin-like modifier activating enzyme 5) belongs to the ubiquitin-activating E1 family and UBA5 subfamily. Ubiquitin and ubiquitin-like proteins are known to be covalently conjugated to a variety of cellular substrates via a three-step enzymatic pathway. The ubiquitin-activating enzyme (E1) plays a key role in the first step of ubiquitination pathway to activate ubiquitin or ubiquitin-like proteins. UBA5 had been proved to activate an ubiquitin-like protein, ubiquitin-fold modifier 1 (Ufm1), by forming a high-energy thioester bond. It localizes mainly in cytoplasm, while it mainly localizes to the nucleus in presence of SUMO2. Recombinant human UBA5 protein, fused to His-tag at N-terminus, was expressed in E.coli and purified by using conventional chromatography techniques.