Split‐BioID: a proximity biotinylation assay for dimerization‐dependent protein interactions

The biotin identification (BioID) protocol uses a mutant of the biotin ligase BirA (BirA*) fused to a protein-of-interest to biotinylate proximate proteins in intact cells. Here, we show that two inactive halves of BirA* separately fused to a catalytic and regulatory subunit of protein phosphatase PP1 reconstitute a functional BirA* enzyme upon heterodimerization of the phosphatase subunits. We also demonstrate that this BirA* fragment complementation approach, termed split-BioID, can be used to screen for substrates and other protein interactors of PP1 holoenzymes. Split-BioID is a novel and versatile tool for the identification of (transient) interactors of protein dimers.