ubiquitin reconstruction PSI-MI myth The split-ubiquitin system provides a method for examining the interactions of membrane proteins. In the split-ubiquitin system, two integral membrane proteins to be studied are fused to two different ubiquitin moieties: a C-terminal ubiquitin moiety ("Cub", residues 35-76) and an N-terminal ubiquitin moiety ("Nub", residues 1-34). These fused proteins are called the bait and prey, respectively. In addition to being fused to an integral membrane protein, the Cub moiety is also fused to a transcription factor that can be cleaved off by ubiquitin specific proteases. Upon bait-prey interaction, Nub and Cub-moieties assemble, reconstituting the split-ubiquitin. The reconstituted split-ubiquitin molecule is recognized by ubiquitin specific proteases, which cleave off the reporter protein, allowing it to induce the transcription of reporter genes. ub reconstruction MI:0112 membrane yeast two-hybrid split-ubiquitin membrane two hybrid