Detection and modulation in vivo of helix-loop-helix protein-protein interactions

Studies are described that allow for the in vivo detection of helix-loop- helix (HLH) protein-protein interaction. The assay used requires HLH protein- protein interaction to reconstitute a functional GAL4 transcriptional activator, which in turn activates a reporter gene placed downstream of GAL4 DNA binding sequences. Using this assay, we are able to detect intracellular heterodimerization but not homodimerization of the MyoD, E12, and Id gene products. In addition, using this system we are unable to detect stable heterodimerization between MyoD and c-Jun. We also show that expression of activated ras(H) gene product does not inhibit and may stabilize HLH protein- protein interaction. This system may be of general utility in studying the modulation of transcription factor interactions.