Novel 130‐kDa rat liver myosin‐1 will translocate actin filaments

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Abstract
We have recently purified and characterized from rat liver, polypeptides of 110‐kDa and 130‐kDa which possess several characteristics of myosin‐1 [Coluccio and Conaty: Cell Motil. Cytoskeleton 24:189‐199, 1993]. What roles these myosin‐1 molecules play in hepatocytes is not yet defined. One hypothesis is that they are involved in either intracellular transport or locomotion. As a first step in establishing their function, we have investigated whether these molecules are capable of supporting motility in vitro. Our results clearly demonstrate that the isolated 130‐kDa‐calmodulin complex will translocate filaments at a rate of 0.03‐0.05 μ/sec; motility is inhibited in free calcium ion concentrations above 0.1 μM. This inhibition is reversed with the addition of exogenous calmodulin. These results provide supporting evidence of a motile role for the 130‐kDa‐calmodulin complex in vivo. This is the first demonstration that in higher eukaryotes, myosin‐1 from a tissue other than intestine will support motility. Partial peptide sequence analysis indicates that the 130‐kDa polypeptide resembles the recently described myr 1 [Ruppert et al.: J. Cell Biol. 120:1393‐1403, 1993] or MM1α [Sherr et al.: J. Cell Biol. 1405‐1416, 1993] gene product.