Spectrin, an actin binding protein that is a major component of the cytoskeletal superstructure of the erythrocyte plasma membrane, is essential in determining the properties of the membrane including its shape and deformability. Spectrins function as membrane organizers and stabilizers, composed of nonhomologous Alpha and beta chains, which aggregate side-to-side in an antiparallel fashion to form dimers, tetramers, and higher polymers. The spectrin tetramers in erythrocytes act as barriers to lateral diffusion, but spectrin dimers seem to lack this function. Spectrin beta IV is a non-erythrocytic member of the beta-spectrin family. It is expressed in brain and pancreatic islets and localizes to the nuclear matrix, cytoplasmic vesicles and PML nuclear bodies. Spectrin beta IV is a 2,564 amino acid protein with four isoforms due to alternative splicing events.