Human HR23A/Rad23A has two ubiquitin-associated (UBA) motifs that can each bind ubiquitin via a hydrophobic surface formed by residues located within the alpha1 and alpha3 helices of each UBA domain. Tandem-repeated ubiquitin binding entities (TUBEs), which consist of multiple tandem ubiquitin-binding UBA motifs, have been developed for the isolation and identification of ubiquitinated proteins. TUBEs show increased affinity for poly-ubiquitin moieties compared to single UBA motifs. Additionally, TUBEs protect polyubiquitinated proteins from deubiquitylating enzymes, allowing for the detection of polyubiquitinated proteins at relatively low levels of abundance.