Domain structure of the myosin head in correlation-averaged images of shadowed molecules

Electron microscope images of rotary shadowed myosin heads and subfragment-1 (S1) have been computationally aligned and averaged using correlation methods. Average images show reproducible detail within the 'pear-shaped' envelope of the head; the major features are invariant in S1 and in intact heads, in two mirror-related views of the head, and in the presence and absence of ATP. The averages support the view that the head contains two main structural domains separated by a cleft, and that the region of the neck close to the head-rod junction is flexible. They also reveal the inadequacy of the conventional method of correcting the measured dimensions of shadowed particles for the supposed thickness of the 'metal coat'.