A method of identifying proteins able to interact via protein-protein interactions with a protein of interest, comprising (a) performing a first assay to identify cells expressing a reporter gene, wherein the first assay is transcription-based two-hybrid screening system; (b) obtaining DNA from the cells identified in step (a) via a PCR procedure; and (c) performing a second assay on the DNA obtained in step (b), wherein the second assay is a non-transcription-based two-hybrid screening system, to identify cells expressing a reporter gene, wherein positive cells identified in step (a) that are found to be positive in step (c) express a protein able to interact via protein-protein interactions with a protein of interest.