The yeast tribrid system--genetic detection of trans-phosphorylated ITAM-SH2-interactions.

Protein-protein interactions are often dependent on the post-translational modification of one component of a complex. To facilitate the study of these interactions in signal transduction, we have developed the yeast tribrid system, a modification of the yeast two-hybrid system. We demonstrate that the interactions are dependent upon the presence of a tyrosine kinase, an SH2 domain and a tyrosine containing substrate. Using the gamma subunit of the high-affinity IgE receptor, Fc epsilon RI, this approach has been used to isolate a novel SH2-containing family member. The mRNA encoding this novel protein is differentially expressed in rat tissues. The yeast tribrid system can be readily adapted for the characterization of novel tyrosine kinases or substrates, as well as the study of protein-protein interactions which involve other post-translational modifications.