A method of crystallographic analysis to identify myosin heads interac
ting with specific actin sites in vertebrate striated muscles is descr
ibed. It is based on a Fourier transform of a helix in which probabili
ty of occurrence of subunits varies periodically. It predicts the pres
ence of layer-lines at 1/24 and 1/10.4 nm(-1) which are experimentally
observed in contracting and rigor vertebrate striated muscles, showin
g that the myosin heads are interacting with specific sites on actin b
ut are still maintaining their average 14.5 nm axial periodicity.