A protein that interacts with myosin to form the contractile protein actomyosin in muscles, which is involved in other physiological processes (e.g., cellular movement, maintenance of cell shape) in the form of other contractile elements such as flagella. It can exist in a globular or a fibrous form, and is the most abundant protein in the typical eukaryotic cell, accounting for about 15 percent in some cell types. In fibrous form, an actin filament is about 5 nm wide and 100 um long, and attaches itself to transverse Z filaments in the muscle fiber.
See Actomyosin, Adenosine triphosphosphate (ATP), Cytoplasm, Cytoskeleton, Eukaryote cell (or organism), Extrafusal muscle fibers, Flagella, Intrafusal muscle fibers, Limkinase 1 gene, Myofibrils and myofilaments, Myosin, Muscle fiber, Sarcomere