Ubiquitin-interactor co-pulldown coupled with mass spectrometry used to elucidate K48- and K63-linked interactomes including those of Ub chains of varying length (Ub-Ub3) and heterotypic branched Ub chains. Ubiquitin-interactors were enriched from human HeLa and yeast s. cerevisiae cell lysate with either chloroacetamide (CAA) or N-ethylmaleimide (NEM) as DUB inhibitors.