Three-dimensional image analysis of the complex of thin filaments and myosin molecules from skeletal muscle. IV. Reconstitution from minimal- and high-dose images of the actin-tropomyosin-myosin subfragment-1 complex.

Three-dimensional images of the actin-tropomyosin-myosin subfragment-1 (S1) complex were reconstituted from both minimal- and high-dose electron micrographs by using a conventional reconstruction technique. Higher resolution (1/15 A-1) than those of the previous reconstructions was attained. A multi-domain structure similar to that of the actin-S1 complex described in the previous paper (1) was observed and a ne diagram of the multi-domain structure of the actin-tropomyosin-S1 complex is presented. The shape of S1 molecules in the rigor complex was clearly resolved. In a view perpendicular to the filament axis, S1 had an axially bent profile; only the tail portion, which was thin but was not small in diameter, was steeply inclined. These features were more prominent in the model from minimal-dose images than that from high-dose images.