ANALYSIS OF A CORTICAL CYTOSKELETAL STRUCTURE - A ROLE FOR EZRIN-RADIXIN-MOESIN (ERM PROTEINS) IN THE MARGINAL BAND OF CHICKEN ERYTHROCYTES

We are studying how the cytoskeleton determines cell shape, using a si mple model system, the marginal band of chicken erythrocytes. We previ ously identified a minor component of the marginal band by a monoclona l antibody, called 13H9 (Birgbauer and Solomon (1989). J. Cell Biol. 1 09, 1609-1620; Goslin et al. (1989). J. Cell Biol. 109, 1621-1631). mA b 13H9 also binds to the leading edges of fibroblasts and to neuronal growth cones and recognizes the cytoskeletal protein ezrin. In,recent years, two proteins with a high degree of homology to ezrin were ident ified: moesin and radixin, together comprising the ERM protein family. We now show that the contiguous epitope sufficient for mAb 13H9 bindi ng is a sequence present in each of the ERM proteins, as well as the p roduct of the gene associated with neurofibromatosis 2, merlin or schw annomin. We used biochemical and immunological techniques, as well as PCR to characterize the expression and localization of the ERM protein s in chicken erythrocytes. The results demonstrate that radixin is the major ERM protein associated with the cytoskeleton. Both ezrin and ra dixin localize to the position of the marginal band. Our results sugge st that the ERM proteins play functionally conserved roles in quite di verse organelles.