Our results also suggest the involvement of K48/K63 branched Ub in Huntington’s disease, as we identified the huntingtin-interacting protein HIP1 and UBR4, which has been linked to K11/K48 branched ubiquitination on mutant huntingtin (68), as specific interactors of Br Ub3. Here, UBR4 is linked to Huntington disease.