Actin is one of the most abundant and highly conserved proteins of eukaryotes (1-5). Mammalian actins are the product of six distinct but closely related genes with differing distribution patterns in cell types and in tissues. The amino acid sequences of the six human actin gene products are 94-97% identical, so antibodies which bind all six gene products are to be expected. A sequence alignment of the six human actin can be downloaded from here. The molecular weight of all six proteins is ~42kDa, and one or more actins is found in essentially every type of crude cellular and tissue extract. As a result, antibodies to actin are widely used as western blotting standards to verify that the various steps of the western blotting procedure have been performed correctly. In addition, actin is regarded as a “house keeping” protein This antibody pan-specific actin and recognizes six human actin proteins expressed in bacteria.