Generation of diversity in nonerythroid spectrins. Multiple polypeptides are predicted by sequence analysis of cDNAs encompassing the coding region of human nonerythroid alpha-spectrin

Nonerythroid alpha-spectrin (alpha-fodrin) is a major component of the membrane skeleton in diverse cell types. Overlapping cDNAs have been isolated which encompass the coding region of human lung fibroblast nonerythroid alpha-spectrin. The composite sequence of 7,787 nucleotides encodes a polypeptide of 2,472 amino acids (predicted Mr of 283,964). This sequence has 58% amino acid identity with human erythroid alpha-spectrin, which is encoded on a different gene, and 96% amino acid identity with the full-length sequence of chicken brain alpha-spectrin. We previously reported the variable expression in human fibroblast alpha-spectrin of 20 amino acids between repeats 10 and 11 (McMahon, A. P., Giebelhaus, D. H., Champion, J. E., Bailes, J. A., Lacey, S., Carritt, B., Henchman, S. K., and Moon, R. T. (1987) Differentiation 34, 68-78). In this study, we report additional heterogeneity in fibroblast alpha-spectrin near the carboxyl-terminal end. One of the fibroblast cDNAs (clone 3D) has an in-frame deletion of 18 nucleotides within spectrin repeat 21 when compared to an overlapping fibroblast cDNA (clone 7). As this heterogeneity in amino acid sequence occurs near domains of nonerythroid alpha-spectrin suggested to bind calcium or actin, it is possible that fibroblasts express functionally distinct isoforms of nonerythroid alpha-spectrin.