Abstract
Myosin has been isolated from cloned mouse fibroblasts, line L-929. Fibroblast myosin: (i) binds to rabbit muscle actin and is dissociated from it by ATP, (ii) has an ATPase activity that is suppressed by Mg(2+) in 0.6 M KCl and is activated by rabbit muscle actin in the presence of Mg(2+) in 14 mM KCl, (iii) forms thin bipolar aggregates in 0.1 M KCl when viewed in the electron microscope, (iv) possesses a heavy chain with the same mobility as muscle myosin (molecular weight 200,000) in sodium dodecyl sulfate-polyacrylamide gel electrophoresis. In these respects, fibroblast myosin appears to be similar to muscle myosin in structure and function.