Probably plays a role in the formation and regulation of the tight junction (TJ) paracellular permeability barrier, possibly by linking ZO proteins to the actomyosin cytoskeleton. Parallel homodimer (PubMed:10613913). Interacts with TJP1/ZO1 and TJP2/ZO2 in vivo, and TJP3/ZO3, myosin and OCLN in vitro, possibly directly (PubMed:10613913, PubMed:10491082, PubMed:12023291). Acts as an F-actin bundling protein in vitro (PubMed:11682052). Localizes to the apical junction complex composed of tight and adherens junctions. Localized on the cytoplasmic face of tight junctions of polarized epithelia and some endothelia. A maternally synthesized protein. Found in the apical cortex in the fertilized egg, where it is associated with cytoskeleton filaments, it is recruited to tight junctions before TJP1/ZO1 and OCLN. Nascent tight junctions are in place by the two-cell stage. Deletion of the TJP1/ZO1 interaction motif (ZIM) decreases but does not abolish colocalization with TJP1/ZO1. Belongs to the cingulin family. It is uncertain whether Met-1 or Met-9 is the initiator. Truncated N-terminus.