Complex sentence: Dimeric spectrin is formed by the lateral association of αI and βI monomers to form a dimer, dimers then associate in a head-to-head formation to produce the tetramer.
Split into simpler sentences: Dimeric spectrin is formed by the lateral association of αI and βI monomers to form a dimer. Dimers then associate in a head-to-head formation to produce the tetramer.