Fig. 7. Model of in situ PEVK-actin interaction in the sarcomere. Schematic arrangement of myofilaments in an extended and contracted sarcomere. Top panel, highly extended sarcomere. Middle panel, shortening sarcomere in which the PEVK domain is contracted. Bottom panel, shortening sarcomere in which the tip of the thick filament crossed the site of PEVK binding to the thin filament. The shaded area indicates the dimensions of the space occupied by the PEVK domain that defines the apparent concentration of the actin-binding sites in PEVK. As the dimensions of this space vary along the thin filament axis, the actin concentration is constant regardless of the size of the space. Arrows indicate the direction of movement during the contraction of a rather thick filament.