FIGURE 1.

(a) Domain/repeat structure of α- and β-spectrin (after Speicher (18)). The α- and β-units occur in antiparallel side-to-side orientation to form heterodimers that then associate via head-to-head association to form tetramers making up the segments involved within a spoked JC. Most repeat units (indicated by rectangles) are homologous and are 106 residues in length. The repeats are composed of triply folded α-helices. Repeats are connected by short linker peptides indicated in green. Nonhomologous segments are indicated by squares and have different lengths. Domains are indicated by Roman numerals and were derived via digestion and were established before amino-terminal orientation of the subunits were established. (b) Schematic illustrating a folded repeated Sp structure comprised mostly of the 106-residue repeats, and a peptide segment in which one repeat has unfolded.