Biochemical, Immunochemical and Immunohistochemical Identification of Myosin Heavy Chains in Cultured Cells of Catharanthus roseus

In the pollen tubes of the lily Lilium longiflorum, myosin,composed of 170-kDa heavy chains is responsible for the intracellulartransport of organelles Yokota and Shimmen (1994) Protoplasma177: 153]. Polypeptides of 170 kDa with similar antigenicityto this pollen-tube myosin have also been found in other angiospermcells Yokota et al. (1995) Protoplasma 185: 178]. To clarifythe role of this type of myosin in cytoplasmic streaming, weprepared partially purified myosin fraction from cultured cellsof Catharanthus roseus by co-precipitation with F-actin. Ina motility assay in vitro with this fraction, rhodamine-phalloidin-labeledF-actin moved with an average velocity of 10.7 µm s^-1.This sliding velocity was similar to that of the cytoplasmicstreaming observed in intact cultured cells. Antibodies raisedagainst the 170-kDa heavy chain of pollen-tube myosin recognizedonly a single polypeptide of 170 kDa in this partially purifiedfraction. The same polypeptide was also identified by theseantibodies in a crude extract of proteins from cultured cells.The myosin-specific fluorescence was concentrated around thenuclei and was associated with particles of various sizes. Duallocalization using antibodies against myosin and against actinrevealed that these particles were preferentially co-localizedwith actin filaments. On the other hand, no component of thecrude extract or of the partially purified myosin fraction cross-reactedwith antibodies against heavy chains of myosin II from animalcells. These results suggest that the 170-kDa polypeptide is the myosinheavy chain and that this myosin generates the motive forcefor cytoplasmic streaming in cultured cells of Catharanthusroseus. (Received March 28, 1995; Accepted September 14, 1995)