Adapter protein involved in asymmetrical cell division and cell polarization processes. Probably involved in the formation of epithelial tight junctions. Association with PARD3 may prevent the interaction of PARD3 with F11R/JAM1, thereby preventing tight junction assembly. The PARD6-PARD3 complex links GTP-bound Rho small GTPases to atypical protein kinase C proteins (PubMed:10873802). Regulates centrosome organization and function. Essential for the centrosomal recruitment of key proteins that control centrosomal microtubule organization (PubMed:20719959). {ECO:0000269|PubMed:10873802, ECO:0000269|PubMed:20719959}. This is the function of PARD6A (par-6 family cell polarity regulator alpha, ENSG00000102981).