INTERCHAIN BINDING AT THE TAIL END OF THE DROSOPHILA SPECTRIN MOLECULE

Spectrin's function as an actin-crosslinking protein and membrane skel eton component involves the tail end of the molecule, where multiple i nteractions between two spectrin chains and between these chains and o ther proteins give rise to complexes that form membrane skeleton netwo rk junctions. To determine whether the sequences that contribute to in terchain binding can be distinguished from sequences that are involved in other spectrin tail end functions, we mapped the regions in each D rosophila spectrin chain that are required for interchain binding in v itro. Segments 20 and 21 of the alpha chain and 2 and 3 of the beta ch ain are required for binding. Binding appears to be very dependent on the lateral register of segments in the two apposed chains. Domains of the nonrepetitive segments, 22 of alpha chain and 1 of beta chain, ar e also involved in associating the two chains. Required sequences with in these nonrepetitive segments are interspersed within domains that a re known to be involved in associations with other Structural proteins , such as actin, and regulatory components, such as protein 4.1 and ca lcium.