UBA5 is a member of the ubiquitin-activating E1 family and UBA5 subfamily. Ubiquitin and ubiquitin-like proteins are recognized as covalently conjugated to various cellular substrates by a three-step enzymatic pathway. The ubiquitin-activating enzyme (E1) has a vital role in the first step of ubiquitination pathway to activate ubiquitin or ubiquitin-like proteins. UBA5 activates ubiquitin-fold modifier 1, a ubiquitin-like post-translational modifier protein, via the formation of a high-energy thioester bond. UBA5 is located primarily in cytoplasm, while it generally localizes to the nucleus in presence of SUMO2.