Myosin is a hexamer of 2 heavy chains and 4 light chains (two regulatory light chains and two essential light chains). The sequences of all three RMLC calcium-binding domains have diverged significantly from that of calmodulin. Therefore, it seems unlikely that these light chains bind calcium. It is potential that phosphorylation has taken over the role of calcium-binding in the regulation of Dictyostelium myosin. In D.discoideum, cAMP stimulation induces RMLC phosphorylation; this chain is phosphorylated on a serine residue.