Myosin regulatory subunit that plays an important role in regulation of both smooth muscle and nonmuscle cell contractile activity via its phosphorylation. Phosphorylation triggers actin polymerization in vascular smooth muscle. Implicated in cytokinesis, receptor capping, and cell locomotion. Myosin is a hexamer of 2 heavy chains and 4 light chains: interacts with myosin heavy chain MYO19. Ubiquitously expressed in various hematopoietic cells. Phosphorylation increases the actin-activated myosin ATPase activity and thereby regulates the contractile activity. It is required to generate the driving force in the migration of the cells but not necessary for localization of myosin-2 at the leading edge. Phosphorylation is reduced following epigallocatechin-3-O-gallate treatment. This chain binds calcium.