Actin-based motor protein, possibly involved in a wide range of motile processes, such as cell movement across a surface, and extension and retraction of pseudopodia or lamellipodia. Myosin I heavy chain is single-headed. Dimer of a heavy and a light chain. Inability to self-assemble into filaments. Belongs to the TRAFAC class myosin-kinesin ATPase superfamily. Myosin family.