cDNA cloning, characterization, and chromosome mapping of UBE2E3 (alias UbcH9), encoding an N-terminally extended human ubiquitin-conjugating enzyme.

A cDNA encoding a third member of human class III ubiquitin-conjugating enzymes (E2s), UBE2E3, was cloned from a human gastric adenocarcinoma cDNA library. The deduced 207-amino acid protein shares over 94% amino acid identity with the UBC domains of class III E2s, UbcH6, UBE2E2, UbcM2, UbcM3, and UbcD2. But the N-terminal extension exhibited little homology among these, except for UbcM2, which showed 100% identity, and which is thought to be a mouse counterpart. Northern hybridization analysis exhibited a strong 1.9-kb band of UBE2E3 in skeletal muscle. Recombinant fusion protein of GST-UBE2E3 was found to form a thioester bond with ubiquitin (Ub) in an E1-dependent manner, demonstrating that the cDNA encodes a functional E2. In addition, a UBE2E3 mutant of cysteine-145 to serine failed in UBE2E3-Ub complex formation, indicating that the cysteine is essential for E2 function. Using FISH and PCR analysis of radiation hybrid and somatic cell hybrid panels the UBE2E3 gene was mapped to human chromosome 2q32.1 and showed strong linkage to SHGC-8506 (LOD = 11.52) between D2S1302 and D2S364.