A novel indication of the activities of small molecule inhibitors of protein-protein interactions: application of the yeast two-hybrid system.

Numerous cellular processes, such as signal transduction and protein transport, are regulated through protein-protein interactions1). To reveal the roles of these interactions in vivo, it is important to investigate the effect of inhibition of each protein-protein interaction. Small molecule inhibitors of protein-protein interactions are useful for such purposes, but only a few inhibitors have been identified2,3). The lack of effective screening methods may be a main reason for this situation. The possible application of the yeast two-hybrid system for identifying small molecule inhibitors of protein-protein interactions was suggested by FIELDS and STERNGLANZ4). In the original yeast two-hybrid system, protein-protein interaction in yeast leads to the expression of a reporter gene HIS3, which permits the yeast to grow without histidine. Therefore, small molecule inhibitors of the protein-protein interactions can be selected as growth inhibitors of the yeast in the medium without histidine. However, this principle is impractical itself, because growth inhibitors, such as protein synthesis inhibitors, DNA synthesis inhibitors and respiration inhibitors, would also be selected in the actual screening and are difficult to exclude. We predicted that the true inhibitors of protein-protein interactions should inhibit the growth of the yeast in the medium without histidine but not in that with histidine.