Ubiquitin-protein ligase E3A (UBE3A) also known as E6AP ubiquitin-protein ligase (E6AP) is an enzyme that in humans is encoded by the UBE3A gene. This enzyme is involved in targeting proteins for degradation within cells. Protein degradation is a normal process that removes damaged or unnecessary proteins and helps maintain the normal functions of cells.Ubiquitin protein ligase E3A attaches a small marker protein called ubiquitin to proteins that should be degraded. Cellular structures called proteasomes recognize and digest proteins tagged with ubiquitin.