Sonic vibration induces the nucleation of actin in the absence of magnesium ions and cytochalasins inhibit the elongation of the nuclei.

Polymerization of actin was completely inhibited by metal chelating agents, such as EDTA or diaminocyclohexanetetraacetic acid, even in the presence of 0.1 M KCl and excess ATP. Addition of 1 mM MgCl2, but not CaCl2, caused full polymerization in the presence of 10 mM diaminocyclohexanetetraacetic acid, suggesting that micromolar concentrations of Mg ions are required for the polymerization of actin. However, it turned out that sonic vibration induced a very rapid polymerization of actin in the absence of Mg ions. The sonication-induced polymerization of actin was greatly inhibited by cytochalasins D and B, and partially by beta-actinin. This can be explained by assuming that the fast growing ends of the formed nuclei are blocked by the cytochalasins, and the slowly growing ends with beta-actinin. The elongation of added F-actin fragments was also similarly inhibited by the cytochalasins and beta-actinin in the absence of Mg ions. It appears that sonic vibration enhances nuclei formation of actin monomers by mechanical agitation in the absence of Mg ions, which stabilize formed nuclei.