FIGURE 4.

Bundles do not dissociate even over long time scales. A–F, one long filament was attached in the middle to a bead, and the ends were allowed to form a bundle in the presence of 0.1 μm α-actinin. After bundle formation, the bundle was moved into the buffer lane, and all other flow lanes were turned off. The bundle was observed periodically over 40 min. The filaments were never observed to separate (supplemental Movie S8) This experiment was replicated six times with the same results, using bundles derived from one to three filaments (two to three lengths of filaments incorporated into the bundle). G–L, two filaments were attached to a bead, and the same experiment was performed using 0.1 μm fascin. As with α-actinin, the fascin bundles were extremely stable, showing no dissociation over 40-min observations. This experiment was replicated six times using two and three filaments in the bundle (supplemental Movie S9). Additional material on this experiment is found in supplemental Figs. S3 and S4 and supplemental Movies S10–S13.