Myosin is a protein that binds to F-actin and has ATPase activity that is activated by F-actin. Myosin I heavy chain is single-headed. Dimer of a heavy and a light chain. Inability to self-assemble into filaments. Myosin tail domain binds directly to anionic phospholipid membranes; myosins I could therefore move actin relative to membranes and vice versa. TH.2 and SH3 bind tightly to F-actin; this together with the nucleotide-sensitive site in the head, allows single molecules of myosin I to cross-link actin filaments. This organism expresses at least three isoforms of myosin I heavy-chain, encoded by genes MIA, MIB, and MIC. Belongs to the TRAFAC class myosin-kinesin ATPase superfamily. Myosin family. Was originally thought to be myosin IB.