Polylysine was found to induce polymerization of muscle actin in a low ionic strength buffer containing 0.4 mM MgCl2. The rate of induced polymerization was dependent on the amount and on the molecular size of the polylysine added. A similar effect was obtained by adding actin nuclei (containing about 2-4 actin subunits) cross-linked by p-NN′-phenylenebismaleimide to G-actin under the same conditions, suggesting that the effect ofpolylysine is due to promotion of the formation of actin nuclei. Polymerization induced by polylysine and by crosslinked actin nuclei was inhibited by low concentrations (10-8-10-6 M) of cytochalasins. Binding experiments showed that actin filaments, but not actin monomers, contained high-affinity binding sites for [3H]cytochalasin B (one site per 600 actin monomers). The relative affinity of several cytochalasins for these sites (determined by competitive displacement of [3H]dihydrocytochalasin B) was: cytochalasin D > cytochalasin E ≅ dihydrocytochalasin B. The results of this study suggest that cytochalasins inhibit nuclei-induced actin polymerization by binding to highly specific sites at the point of monomer addition, i.e., the elongation site, in actin nuclei and filaments.
All Science Journal Classification (ASJC) codes
- Cell Biology
- Actin filaments
- Actin polymerization
- Cell motility