A wide variety of methods used in the study of signal transduction in eukaryotes rely on the ability to precipitate proteins from whole cell extracts. Immunoprecipitation and related methods of affinity purification are routinely used to assess binding partner interactions and enzyme activity in addition to the size of a protein, rates of protein synthesis and turnover, and protein abundance, thus making it a mainstay of a wide variety of protocols. This chapter will provide starting-point methods for immunoprecipitation of proteins under denaturing and nondenaturing conditions and the detection of protein-protein interactions by co-precipitation. The Notes section gives recommendations on how to troubleshoot potential problems that can arise while doing these methodologies.
