Methods and a kit are provided for characterizing small molecules from a library of small molecules or alternatively identifying protein targets to which known small molecules bind. The methods include forming hybrid ligand in which at least one ligand is a small molecule. The hybrid ligand is introduced into cells that in turn contain a first and a second expression vector. Each expression vector includes DNA for expressing a hybrid protein that encodes a target protein linked to a coding sequence for a transcriptional module. The cells further contains a reporter gene, the expression of which is conditioned on the proximity of the first and second hybrid proteins to each other, an event that occurs only if the hybrid ligand binds to target sites on both hybrid proteins. Those cell which express the reporter gene are selected and the unknown small molecule or the unknown hybrid protein is identified.
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