HUNTINGTIN IS UBIQUITINATED AND INTERACTS WITH A SPECIFIC UBIQUITIN-CONJUGATING ENZYME

Using the yeast two-hybrid system, we have identified a human ubiquiti n-conjugating enzyme (hE2-25K) as a protein that interacts with the ge ne product for Huntington disease (HD) (Huntingtin). This protein has complete amino acid identity with the bovine E2-25K protein and has st riking similarity to the UBC-1, -4 and -5 enzymes of Saccharomyces cer evisiae. This protein is highly expressed in brain and a slightly larg er protein recognized by an anti-E2-25K polyclonal antibody is selecti vely expressed in brain regions affected in HD. The huntingtin-E2-25K interaction is not obviously modulated by CAG length. We also demonstr ate that huntingtin is ubiquitinated. These findings have implications for the regulated catabolism of the gene product for HD.