Progress and variations in two-hybrid and three-hybrid technologies

The original yeast two-hybrid system and its variants have proven to be eff ective tools for identification and analysis of protein-protein, protein-DN A and protein-RNA interactions. The two-hybrid assay is being applied to th e entire complement of proteins of the yeast Saccharomyces cerevisiae to ch aracterize the network of protein-protein interactions in the eukaryotic ce ll. The development of nontranscriptional cytosolic and membrane-associated two-hybrid methods has made it possible to detect and examine a number of protein-protein interactions in their normal cellular locations. Small-mole cule hybrid systems have been developed which can be used to study protein- ligand interactions and to activate cellular processes by forcing protein a ssociations.