Abstract
Work in many laboratories on actin polymerization and the accessory proteins that regulate its assembly has progressed to the stage where we now can focus in detail on the structures and mechanisms of action of these essential protein components of the cytoplasmic matrix. The overall mechanism of actin polymerization is clear and the rate constants for the main steps are known. The inventory of the regulatory proteins is now large enough that we likely have in hand, from one cell or another, representatives of the major functional classes. The primary structures of actin and many of the regulatory proteins are known and their mechanisms of action partially deciphered. The long- term goal of research in the field is to provide an explanation at the molecular and cellular levels of how the actin system is assembled and remodeled during the life of the cell.