Linkages of the cytoskeleton to integral membrane proteins of the plasma membrane have been shown to be important for diverse cellular functions. The erythrocyte membrane provides the best studied example of how the spectrin-actin based membrane cytoskeleton is linked via two proteins, ankyrin and protein 4.1, to the anion exchanger (anion exchanger 1, AE1). Although these and other types of cytoskeleton-membrane connections have been well documented by in vitro binding studies it has not been possible to establish any of such interactions by defining the binding interface at the amino acid level. In the present study we have performed binding studies between protein 4.1 and AE1 using peptides and corresponding idiotypic and anti-idiotypic antibodies to show that arginine-rich clusters of the cytoplasmic domain of AE1 (IRRRY/LRRRY) serve as a major binding site for a motif with opposite charge and identical hydrophobicity present on the membrane-binding domain of protein 4.1 (LEEDY). Both motifs appear to be highly conserved during evolution and may also be involved in other types of cytoskeleton-membrane association, i.e. in binding of protein 4.1 to the glycophorins.