Polymerized (F-) actin is induced to form bundles by a number of polycations including
divalent metal ions, Co (NH), and basic polypeptides. The general features of bundle
formation are largely independent of the specific structure of the bundling agent used. A
threshold concentration of polycation is required to form lateral aggregates of actin filaments.
The threshold concentration varies strongly with the valence of the cation and increases with
the ionic strength of the solution. Polyanions such as nucleoside phosphates or oligomers of …