Ubiquitin conjugation factor E4 A is a protein that in humans is encoded by the UBE4A gene.

This gene encodes a member of the U-box ubiquitin ligase family. The encoded protein is involved in multiubiquitin chain assembly and plays a critical role in chromosome condensation and separation through the polyubiquitination of securin. Autoantibodies against the encoded protein may be markers for scleroderma and Crohn's disease. A pseudogene of this gene is located on the long arm of chromosome 3. Alternatively spliced transcript variants encoding multiple isoforms have been observed for this gene. [provided by RefSeq].
Function: Binds to the ubiquitin moieties of preformed conjugates and catalyzes ubiquitin chain assembly in conjunction with E1, E2, and E3 (By similarity).