  We discuss a theoretical model for the cooperative binding dynamics of
tropomyosin to actin filaments. Tropomyosin binds to actin by occupying seven
consecutive monomers. The model includes a strong attraction between attached
tropomyosin molecules. We start with an empty lattice and show that the binding
goes through several stages. The first stage represents fast initial binding
and leaves many small vacancies between blocks of bound molecules. In the
second stage the vacancies annihilate slowly as tropomyosin molecules detach
and re-attach. Finally the system approaches equilibrium. Using a grain-growth
model and a diffusion-coagulation model we give analytical approximations for
the vacancy density in all regimes.
