Characterization of Myosin Heavy Chain and Its Gene in Amoeba proteus

ABSTRACT Monoclonal antibodies against the myosin heavy chain of Amoeba proteus were obtained and used to localize myosin inside amoebae and to clone cDNAs encoding myosin. Myosin was found throughout the amoeba cytoplasm but was more concentrated in the ectoplasmic regions as determined by indirect immunofluorescence microscopy. In symbiont‐bearing xD amoebae, myosin was also found on the symbiosome membranes, as checked by indirect immunofluorescence microscopy and by immunoelectron microscopy. The open reading frame of a cloned myosin cDNA contained 6,414 nucleotides, coding for a polypeptide of 2,138 amino acids. While the amino‐acid sequence of the globular head region of amoeba's myosin had a high degree of similarity with that of myosins from various organisms, the tail region building a coiled‐coil structure did not show a significant sequence similarity. There appeared to be at least three different isoforms of myosins in amoebae, with closely related amino acids in the globular head region.