RAB13 (Ras-related protein Rab-13) belongs to the small GTPase superfamily. Members of the RAB protein family are nontransforming monomeric GTP-binding proteins of the Ras superfamily that contain 4 highly conserved regions involved in GTP binding and hydrolysis. RAB proteins are also an integral part of endocytic pathways. The GTPase Rab13 regulates the assembly of functional epithelial tight junctions (TJs). It is expressed at all stages of preimplantation development.