The isolation of protein complexes is a powerful method to elucidate how signaling networks are regulated. Co-immunoprecipitation (co-IP) is a widely used procedure to detect and characterize the physical association of pathway components that has frequently been used to reveal mechanisms of pathway regulation. This chapter outlines the roles of protein-protein interactions in signal transduction and the regulatory functions such assemblies impart to cells. The principles behind co-IPs are discussed and best practices for conducting and interpreting co-IPs experiments are outlined. Finally, protocols are presented for detecting protein-protein interactions in cycling cells and in cells progressing through a synchronized cell cycle.
Keywords: Cell cycle; Cell synchronization procedures; Co-immunoprecipitation; Mitotic exit network; Protein complexes; Protein–protein interactions.