Analysis of ubiquitin chain-binding proteins by two-hybrid methods

Ubiquitin (Ub) regulates important cellular processes through covalent attachment to its substrates. Distinct fates are bestowed on multi-Ub chains linked through different lysine residues. Ub contains seven conserved lysines, all of which could be used for multi-Ub chain formation. K29 and K48 are the signals for proteasome-mediated proteolysis. Multi-Ub chains linked through K63 have nonproteolytic functions. Studies of Ub-binding factors are likely the key to understanding diverse functions of the Ub molecule. Yeast two-hybrid assay can be a powerful approach to dissect the interaction between Ub and its binding proteins and also the function of these Ub-chain binding proteins in vivo.