UBB and Huntington disease: In order to confirm or discard the hypothesis that intermediate species as the pathogenic structures in HD, (Bennett et al.)tested the effect of in vitro-generated soluble htt∗ fragments (Bowman et al., 2005), highly aggregated fibrillar species or soluble oligomeric aggregates (Chen and Wetzel, 2001; Poirier et al., 2002) on the degradation of ubiquitin-dependent and ubiquitin-independent substrates by purified 26S proteasomes.