We report the complete sequence of Drosophila alpha-spectrin and show that it is similar to vertebrate nonerythroid spectrins. As in vertebrates, the alpha subunit consists of two large domains of repetitive sequence (segments 1-9 and 11-19) separated by a short nonrepetitive sequence (segment 10). The 106-residue repetitive segments are defined by a consensus sequence of 54 residues. Chicken alpha-spectrin (Wasenius, V.-M., M. Saraste, P. Salven, M. Eramaa, L. Holm, V.-P. Lehto. 1989. J. Cell Biol. 108:79-93) shares 50 of these consensus positions. Through comparison of spectrin and alpha-actinin sequences, we describe a second lineage of spectrin segments (20 and 21) that differs from the 106-residue segments by an 8-residue insertion and by lack of many of the consensus residues. We present a model of spectrin evolution in which the repetitive lineage of spectrin segments and the nonrepetitive lineage of segments found in spectrin and alpha-actinin arose by separate multiplication events.

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