Actin is the most abundant protein found in virtually all eukaryotic cells. It is also one of the most highly-conserved proteins, differing by no more than 20% in species as diverse as algae and humans, making it an excellent choice for use as a loading control. It is the monomeric subunit of microfilaments, one of the three major components of the cytoskeleton, and of thin filaments, which are part of the contractile apparatus in muscle cells. Thus, actin participates in many important cellular functions, including muscle contraction, cell motility, cell division and cytokinesis, vesicle and organelle movement, cell signaling, and the establishment and maintenance of cell junctions and cell shape.
