ISOLATION OF AN AP-1 REPRESSOR BY A NOVEL METHOD FOR DETECTING PROTEIN-PROTEIN INTERACTIONS

Transcription factor AP-1 transduces environmental signals to the tran scriptional machinery. To ensure a quick response yet maintain tight c ontrol over AP-1 target genes, AP-1 activity is likely to be negativel y regulated in nonstimulated cells. To identify proteins that interact with the Jun subunits of AP-1 and repress its activity, we developed a novel screen for detecting protein-protein interactions that is not based on a transcriptional readout. In this system, the mammalian guan yl nucleotide exchange factor (GEF) Sos is recruited to the Saccharomy ces cerevisiae plasma membrane harboring a temperature-sensitive Ras G EF, Cdc25-2, allowing growth at the nonpermissive temperature. Using t he Sos recruitment system, we identified new c-Jun-interacting protein s. One of these, JDP2, heterodimerizes with c-Jun in nonstimulated cel ls and represses AP-1-mediated activation.