Probably plays a role in the formation and regulation of the tight junction (TJ) paracellular permeability barrier. Interacts in vitro with cingulin, possibly directly. Interacts with ZO-1 (By similarity). Localized at tight junctions of both epithelial and endothelial cells. A maternally synthesized protein. Found in granules in the peripheral cytoplasm in the fertilized egg, it localizes first to the basolateral membrane, then to tight junctions after cingulin and ZO-1. Nascent tight junctions are in place by the two-cell stage. The maternal form is more highly phosphorylated than the form detected in later developmental stages. The C-terminus is cytoplasmic and is important for interaction with ZO-1. Necessary for the tight junction localization. Involved in the regulation of the permeability barrier function of the tight junction (By similarity). Phosphorylated. Belongs to the ELL/occludin family.