F-actin cross-linking protein which is thought to anchor actin to a variety of intracellular structures. This is a bundling protein. Increases the actin-stimulated ATPase activity of myosin. Involved in vegetative cell growth, phagocytosis, motility and development, probably through stabilization of the actin network in the cortical cytoskeleton. Homodimer; antiparallel. Expressed diffusely throughout the cytoplasm. Accumulates in the cell cortex, contractile vesicle and phagosome. Expressed throughout development. Levels increase during aggregation (1-6 hours) and are then maintained until late culmination when they start to decrease. Cells show a minor impairment of growth under conditions of reduced temperature and hyperosmotic stress. Fruiting body development and spore production on soil plates is strongly impaired in mutants lacking abpA, but is only mildly affected in mutants on agar plates. Double mutants lacking both abpA and abpC show a marked reduction in growth, cell size and resistance to osmotic shock, and decreased motility and phagocytosis rates. Development is blocked at the tip stage of aggregation, although expression of developmentally regulated genes does not appear to be affected. Double mutants lacking abpA and abpB show a significant reduction in growth and a slight reduction in motility. Development appears to proceed normally until culmination when aberrant fruiting bodies are formed. The phenotypes of the double mutants suggests a partial redundancy in the microfilament system. Belongs to the alpha-actinin family.