Ubiquitin Conjugating Enzyme E2S (UBE2S)

The ubiquitin-proteasome protein degradation pathway involves 3 enzymes: E1, which forms a thioester bond with ubiquitin; E2, which transiently carries the activated ubiquitin molecule as a thioester; and E3, which transfers the activated ubiquitin from the E2 to the substrate. UBE2S behaves as an E2 ubiquitin carrier protein.The longest open reading frame (EPF5-ORF2) encodes a deduced 225-amino acid protein with a calculated molecular mass of 24 kD. It shares 38% identity with yeast Ubc4 and is highly similar to ubiquitin carrier proteins in the core region containing the active-site cysteine. Western blot analysis revealed that EPF serum recognized a much shorter protein encoded by an alternate reading frame, EPF5-ORF1.