The objective of this research is to improve our understanding of the molecular basis of muscle contraction by continuing our studies of the three-dimensional structure of myosin subfragment-1 using single-crystal x-ray diffraction. Myosin is the major protein in muscle, in which it plays both a structural and enzymatic role. The myosin rod forms the backbone of the thick filament, whereas the myosin head is responsible for the generation of movement through the hydrolysis of ATP and its interaction with actin. The long term goal is to characterize all of the conformational intermediates in the contractile cycle which should then form the basis of a molecular mechanism of myosin-based motility.