Critical regions for assembly of vertebrate nonmuscle myosin II.

Myosin II molecules assemble and form filaments through their C-terminal rod region, and the dynamic filament assembly−disassembly process of nonmuscle myosin II molecules is important for cellular activities. To estimate the critical region for filament formation of vertebrate nonmuscle myosin II, we assessed the solubility of a series of truncated recombinant rod fragments of nonmuscle myosin IIB at various concentrations of NaCl. A C-terminal 248-residue rod fragment (Asp 1729−Glu 1976) was shown by its solubility behavior to retain native assembly features, and two regions within it were found to be necessary for assembly:  35 amino acid residues from Asp 1729 to Thr 1763 and 39 amino acid residues from Ala 1875 to Ala 1913, the latter containing a sequence similar to the assembly competence domain (ACD) of skeletal muscle myosin. Fragments lacking either of the two regions were soluble at any NaCl concentration. We referred to these two regions as nonmuscle myosin ACD1 (nACD1) and nACD2, respectively...