"Renaissance" of the Yeast Two-Hybrid System - Enhanced for Automation and High-Throughput to Support Proteome-Wide Research

The recently introduced concept of "interactomics" or "associomics" - defined as the complete repertoire of physical protein-protein interactions (PPIs), ranging from temporary (co-expression of interacting proteins), spatial (cell compartment or specific cell-type existence), conditional (disease-health state) or transient functional pairings to the formation of stable, permanent complexes - presents us with a variety of technical research challenges. Its main bottleneck, however, remains the restricted number of currently available high-throughput screening (HTS) techniques capable of PPI detection. One of the most popular and effective methods is in this context the yeast two-hybrid (Y2H) system which has (despite some undeniable practical limitations) been used in thousands of experimental settings, accounting for the majority of all published PPI data. Therefore, this mini-review summarizes the basic principles and most valuable modifications that have been developed since the introduction of the Y2H system by Fields and Song 20 years ago, and describes its recent expansion towards automation and high-throughput application obligatory for the global investigation of the eukaryotic proteome. Finally, we take a close look at a choice of currently available large-scale analytical strategies (with special emphasis on the human interactome) some of which have already culminated in comprehensive, partly interconnected maps, but which are, nevertheless, still too incomplete to assemble a true picture of all physiologically significant PPIs within the living cell. For this reason, the HTS upgraded Y2H system - in combination with other approaches - will continue to provide an essential tool for the detailed dissection and further characterization of proteome-wide PPIs on a systems biology scale.