Abstract: The present invention relates to a 3-part hybrid system for detection protein interactions in live mammalian cells and screening for compounds modulating such interactions. The method is fully compatible with HTS. The three hybrids are a first heterologous conjugate comprising an anchor protein that specifically binds to an internal structure within the cell conjugated to an interactor protein of type A, a second heterologous conjugate comprising an interactor protein of type B conjugated to the first protein of interest, a third heterologous conjugate comprising a second protein of interest conjugated to a detectable group. When applying a dimerizer compound, interactor proteins A and B bind to each other and if the two proteins of interest interact, the distribution of the detectable group will mimic the distribution of the anchor protein. However, if there is no interaction, the distribution of the detectable group will mimic the distribution of the second protein of interest.