Alpha (240 kd) and Beta (220 kd) spectrin subunits form a spectrin heterodimer that polymerizes and interacts with other proteins, such as ankyrin, to generate a flexible submembranous skeleton. Red cells with spectrin or ankyrin deficiencies are extremely fragile. We have defined the biochemical defects in mice with spectrin deficiencies and sought a probe to analyze the molecular defect. In the process, we have characterized a chicken Alpha spectrin cDNA. The cDNA hybridizes to mRNA from chicken erythroid = chicken nonerythroid greater than mouse nonerythroid much greater than mouse erythroid. Despite the difference between the chicken and the mouse erythroid Alpha spectrin, the translated nucleotide sequence of the chicken cDNA is homologous to the carboxy terminal 1/4 of the human erythroid Alpha spectrin. Similarities include repeating sequences of 106 amino acids, a practically invariant concensus of 19 of the 106 amino acids, and conserved blocks of amino acids with the same hydropathy index. Mouse and human genomic clones have been isolated. In the next five years we will (1) sequence the exons and the intron-exon boundaries of the human spectrin clones to provide information on spectrin gene structure and evolution; (2) map the chromosomal location in the mouse of a Beta spectrin mutation and of the nonerythroid Alpha spectrins to determine the distribution of the spectrin gene family in the genome; (3) quantify and characterize the molecular defects and clone the Alpha spectrin genomic DNA of mice with inherited Alpha spectrin defects caused, all evidence indicates, by lesions at the Alpha spectrin structural locus; and (4) map the chromosomal location of nb, a mutation causing an ankyrin deficiency in mice, and of the ankyrin gene to determine whether the ankyrin lesion is the primary defect.