Actin interacts with a number of so-called actin-binding proteins which participate at various stages of the cell motility process such as regulation of filament formation, assembly and disassembly of filaments, force generation and depolymerization. Gene technology makes a precise mapping of the interacting surfaces on the actin molecules possible by studying specifically designed actin mutants expressed in a suitable organism. In addition, the production of engineered actin will become increasingly important when the three-dimensional structure of actin is determined. Chicken beta-actin can be produced in large quantities in Escherichia coli but such actin shows only a limited biological activity and thus seems to be of minor interest in future studies of structure-function relationships of this molecule. To circumvent the problem of a denatured bacterial protein, the yeast Saccharomyces cerevisiae was chosen as an alternative organism to express actin. This paper describes the expression, isolation and characterization of the yeast-produced chicken beta-actin. From a 12-liter culture of yeast cells, 500 micrograms of polymerizable beta-actin was isolated.