The Tag:FKBP entry in FlyBase represents sequence encoding the Homo sapiens FKBP1A protein (HGNC:3711) where it is used as part of a conditional heterodimerization system. The FKBP1A protein can bind to Tag:FRB in a rapamycin-dependent manner (PMID:8782462, PMID:7539137). This property can be used to bring together two tagged proteins of interest (one tagged with Tag:FRB and the other with Tag:FKBP) in vivo in a rapamycin (or analog)-dependent manner, for example to reconstitute a functional protein by bringing together complementary split system components, or to target a protein of interest to a particular subcellular location.