The PB1 domain found in TFG protein, an oncogenic gene product and fusion partner to nerve growth factor tyrosine kinase receptor TrkA and to the tyrosine kinase ALK. The PB1 domain is a modular domain mediating specific protein-protein interaction in many critical cell processes, such as osteoclastogenesis, angiogenesis, early cardiovascular development and cell polarity. A canonical PB1-PB1 interaction, which involves heterodimerization of two PB1 domains, is required for the formation of macromolecular signaling complexes ensuring specificity and fidelity during cellular signaling. The interaction between two PB1 domain depends on the type of PB1. There are three types of PB1 domains: type I which contains an OPCA motif, acidic aminoacid cluster, type II which contains a basic cluster, and type I/II which contains both an OPCA motif and a basic cluster. The PB1 domains of TFG represent a type I/II PB1 domain. The physiological function of TFG remains unknown.