Structural Biology An isoform of tropomyosin called Tm1-I/C is required for germ cell maturation in Drosophila . This isoform has a low-complexity domain at its carboxy terminus that facilitates assembly into intermediate filaments. The isolated tail domain assembles into polymers that have amyloid-like cross-β structures, but whereas amyloid fibers are extremely stable, these structures are dynamic. Sysoev et al. labeled the tail domain in the context of assembled filaments and used solid-state nuclear magnetic resonance spectroscopy to study its conformation. They again observed the dynamic cross-β structure involving the same sequence as in the isolated tail domain, whereas more than half of the tail remained disordered. There may be other cases in which sequence-specific labile interactions drive the assembly of low-complexity domains to achieve dynamic cellular organization. Proc. Natl. Acad. Sci. U.S.A. 117 , 23510 (2020).