NOVEL 130-KDA RAT-LIVER MYOSIN-1 WILL TRANSLOCATE ACTIN-FILAMENTS

We have recently purified and characterized from rat liver, polypeptid es of 110-kDa and 130-kDa which possess several characteristics of myo sin-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 chat they are involved in either intracellu lar transport or locomotion. As a first step in establishing their fun ction, we have investigated whether these molecules are capable of sup porting motility in vitro. Our results clearly demonstrate that the is olated 130-kDa-calmodulin complex will translocate filaments at a rate of 0.03-0.05 mu m/sec; motility is inhibited in free calcium ion conc entrations above 0.1 mu M. This inhibition is reversed with the additi on of exogenous calmodulin. These results provide supporting evidence of a motile role for the 130-kDa-calmodulin complex in vivo. This is t he first demonstration that in higher eukaryotes, myosin-1 from a tiss ue other than intestine will support motility. Partial peptide sequenc e analysis indicates that the 130-kDa polypeptide resembles the recent ly described myr 1 [Ruppert et al.: J. Cell Biol. 120:1393-1403, 1993] or MM1 alpha [Sherr et al.: J. Cell Biol. 1405-1416, 1993] gene produ ct. (C) 1994 Wiley-Liss, Inc.