Updated project metadata. To facilitate biochemical studies of human cytoplasmic actins, Saccharomyces cerevisiaestrains were developed that express either human β-actin or γ-actin as their sole actin. Actins purified from these strains have biochemical properties similar to mammalian skeletal muscle α-actin, but display differential binding to some key actin regulators. Mass-spectrometry analysis shows that the human actins made from yeast generally retain their N-terminal methionines, which are modified by acetylation.