Studying Protein-Protein Interactions Using a Bacterial Two-Hybrid System

Two-hybrid systems are powerful genetic assays that allow the interaction between two proteins to be detected in vivo. Although originally described in yeast (1 ,2 ), several bacterial two-hybrid systems have recently been developed (reviewed in 3 –6 ). This chapter will describe the use of one such bacterial system: a transcriptional activation-based two-hybrid system for the analysis of protein-protein interactions in Escherichia coli . This system, like the classic yeast two-hybrid system, involves the synthesis of two fusion proteins within the cell whose interaction stimulates expression of a suitable reporter gene. This bacterial system has been used successfully to detect and analyze the interactions between a number of different proteins from both prokaryotes and eukaryotes (7 –10 ), including a phosphorylation-dependent protein-protein interaction between two mammalian transcription factors (11 ), and the interaction between a peptide aptamer and its intracellular target (12 ). The use of selectable reporter genes with this system should facilitate the selection of interacting proteins from complex protein libraries (11 ,13 ).