THE MYOSIN FILAMENT-XV ASSEMBLY - CONTRIBUTIONS OF 195 RESIDUE SEGMENTS OF THE MYOSIN ROD AND THE 8 C-TERMINAL RESIDUES

A mixture of two peptides of approximately M(r) 13000 has been isolate d from a papain digest of LC2 deficient myosin. The peptides assemble into highly ordered aggregates which in one view are made up of strand s of pairs of dots with an average side to side spacing of 13.0 nn and an average axial repeat of 9.0 nm. In another view there are strands of single dots with a side-to-side spacing of 7.8 nm and an axial repe at of 9.1 nm. From N-terminal peptide sequencing, the two peptides hav e been shown to come from regions of the myosin rod displaced by 195 r esidues. We have shown that either peptide alone can assemble to form the same aggregates. The 195 residue displacement of the M(r) 13000 pe ptides corresponds closely to the 196 residue repeat of charges along the myosin rod. This finding permits us to designate 195 residue segme nts of the myosin rod and to relate assembly characteristics directly to the similar 195 residue segments and 196 residue charge repeat. The most C-terminal 195 residue segment carries information for assembly into helical strands. The contiguous 195 residue segment, in major par t, carries information for the unipolar assembly, characteristic of th e assembly in each half of the myosin filament. The next contiguous 19 5 residue segment, in major part, carries information for bipolar asse mbly which is characteristic of the bare zone region of the filament; and for the transition from the bipolar bare zone to unipolar assembly . The effect of the eight C-terminal residues of the myosin rod on the assembly of the contiguous 195 residues has also been studied. The en tire fragment of 195 + eight C-terminal residues assembled to form hel ical strands with an axial repeat of 30 nn. Successive deletion of cha rged residues changed the axial repeat of the helical strands suggesti ng that the charged residues at the C-terminus are involved in determi ning the pitch in the helical assembly of the contiguous 195 residues.