Muscle contraction. Muscle myosin is a hexameric protein that consists of 2 heavy chain subunits (MHC), 2 alkali light chain subunits (MLC) and 2 regulatory light chain subunits (MLC-2). Thick filaments of the myofibrils. Additional isoforms seem to exist. Exons 3, 7, 9, 11 and 15 are mutually exclusive splicing exons and exon 18 is included or excluded. Expressed in larval and adult muscles. Isoforms containing exon 9a are expressed in indirect flight muscles, exons 9a and 9b are expressed in jump muscles, exons 9b and 9c are expressed in other larval and adult muscles. Alternative splicing exons contribute to the specialized contractile activities of different muscle types. Exon 3 encodes the hydrophobic pocket adjacent to the ATP-binding site, exon 9 is adjacent to the actin-binding domain, exon 11 is involved in actin-binding, exon 15 in the S2 hinge and exons 18 and 19 the non-coiled tail region. Limited proteolysis of myosin heavy chain produces 1 light meromyosin (LMM) and 1 heavy meromyosin (HMM). HMM can be further cleaved into 2 globular subfragments (S1) and 1 rod-shaped subfragment (S2). Belongs to the TRAFAC class myosin-kinesin ATPase superfamily. Myosin family.