cDNA cloning, sequencing and chromosome mapping of a non-erythroid spectrin, human α-fodrin

Abstract

Several overlapping cDNA clones encompassing 2760 nucleotides of the α-subunit of a human non-erythroid spectrin (termed fodrin) were isolated from a human lung fibroblast cDNA library. DNA and RNA blot analyses indicated that a single copy α-fodrin gene encodes a 9-kb transcript. The cDNA clones were sequenced, and all were found to contain long open reading frames. The overlapping regions were identical except for a 60-nucleotide in-frame insertion at position 1133 in the composite sequence. This result suggests that at least two distinct transcripts exist in fibroblast cells. The chromosomal location of human α-fodrin was assigned to 1p34–1p36.1 by hybridization to somatic cell hybrids, and it is thus distinct from that of human α-spectrin which has been mapped to 1q22–1q25. Alignment of the composite 919 amino acids of the predicted protein sequence of human α-fodrin with that of human α-spectrin indicated that α-fodrin has a similar 106-amino-acid repeating structure, which is homologous with α-spectrin repeats 7–15. Repeats 10 and 11 are anomalous in sequence and structure from other repeats. A comparison of nucleic acid and amino acid homologies between α-spectrin and the α-fodrin of several vertebrates indicated that human non-erythroid α-fodrin and the common α-subunit of erythroid and non-erythroid cells of non-mammalian vertebrates are closely related (90%-96% amino acid homology), whereas α-fodrin is only distantly related to the erythroid-specific α-spectrin subunit of mammals (55%-59% amino acid homology). These data suggest that mammalian erythroid α-spectrin evolved by duplication and rapid divergence from an ancestral α-fodrin-like gene.

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