Major protein component of the membrane cytoskeleton of mammalian and avian erythroid cells. Responsible for maintaining the normal shape, strength and stability of the erythrocyte. A ubiquitous family of proteins, spectrin analogs have also been isolated from a variety of non-erythroid cells. Given the name spectrin because of its original isolation from hemoglobin-free red cell membranes known as erythrocyte “ghosts”: V. T. Marchesi, E. Steers, Science 159, 203 (1968). Comparison with actin, q.v.: E. Steers, V. Marchesi, J. Gen. Physiol. 54, 65 S (1969). Isoln from human red cells and species comparison: T. W. Tillack et al., Biochim. Biophys. Acta 200, 125 (1970). Spectrin is a heterodimer composed of 2 high mol wt polypeptide subunits referred to as band 1 or α-spectrin (mol wt ≈240 kDa) and band 2 or β-spectrin (mol wt ≈220 kDa). Structural studies: M. Clarke, Biochem. Biophys. Res. Commun. 45, 1063 (1971); T. L. Steck, J. Cell Biol. 62, 1 (1974); J. M. Anderson, J. Biol. Chem. 254, 939 (1979); D. W. Speicher et al., ibid. 257, 9093 (1982). The β-subunit of spectrin is bound to the red cell membrane by proteins known as ankyrin: V. Bennett, P. J. Stenbuck, ibid. 254, 2533 (1979); or syndeins: J. Yu, S. R. Goodman, Proc. Natl. Acad. Sci. USA 76, 2340 (1979). The spectrin heterodimers aggregate on the membrane surface and, together with actin and other proteins, form a filamentous network that covers the surface of the cytoplasmic membrane: S. E. Lux, Nature 281, 426 (1979); idem, Semin. Hematol. 16, 21 (1979). Identification of spectrin analogs from nonerythroid cells: S. R. Goodman et al., Proc. Natl. Acad. Sci. USA 78, 7580 (1981). Isoln of fodrin, also known as brain or neural cell spectrin: J. Levine, M. Willard, J. Cell Biol. 90, 631 (1981); V. Bennett et al., Nature 299, 126 (1982). Isoln of TW 260/240, a spectrin analog from chicken intestinal epithelial cells: J. R. Glenney et al., Cell 28, 843 (1982). Comparison of erythroid and non-erythroid spectrins: J. R. Glenney et al., Proc. Natl. Acad. Sci. USA 79, 4002 (1982); J. R. Glenney, P. Glenney, Eur. J. Biochem. 144, 529 (1984). Review of erythrocyte spectrin: S. R. Goodman, K. Shiffer, Am. J. Physiol. 244, C121-C141 (1983); of neural cell spectrin: S. R. Goodman, I. S. Zagon, ibid. 250, C347-C360 (1986). Comprehensive review: S. R. Goodman et al., Crit. Rev. Biochem. 23, 171-234 (1988).