In 2012, Roux et al. published a nice paper, that received no less than four article recommendations from F1000 researchers. The paper described a method for tracking the interaction partners a protein has had within a cell (a history of its interacting partners). The method, called BioID, is based on proximity-dependent biotinylation of proteins by a promiscuous biotin ligase mutant BirA (R118G), which is fused to your protein of interest. After an overnight incubation with biotin, cells can be subjected to harsh lysis and biotinylated proteins can be isolated and identified by mass spectroscopy to determine the proteins that had come into contact with the chimeric BirA (R118G) protein. This method is a bit different from standard co-IP or pull-down experiments, because it allows one to identify proteins who interact transiently or weakly with the protein of interest. Also, due to the strong biotin-avidin binding affinity, harsh washes can greatly reduce background protein binding.