The Tag:FRB entry in FlyBase represents sequence from the Homo sapiens 'FRAP' (MTOR) gene (HGNC:3942) that encodes an 89 amino acid fragment which is sufficient for binding to the complex formed by the protein encoded by the Homo sapiens FKBP1A gene (HGNC:3711) and rapamycin (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, representing the FKBP1A protein sequence) 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.