Figure 7.

Decoration of F-actin with FLNa molecules. Mixtures of F-actin in the presence or absence of gelsolin were stabilized with phallacidin and incubated with recombinant human FLNa and visualized by low angle metal casting. (A) Representative field of actin filaments both cross-linked and coated with FLNa molecules. The arrowheads identify FLNa molecules attached by one subunit. Bar, 100 nm. (B) Selected images of filaments showing the FLNa–actin interaction. Bar, 100 nm. (C) Quantification of the unbound portion of FLNa associated with the actin filament. The unattached length is approximately equivalent to one subunit (n = 23). Identical experiments with the FLNa truncate FLAG-ABD-IgFLNa1-8 reveal that it attaches only by its ABD (n = 38). (D) Relationship of filament length to the amount of the FLNa molecule associated. Actin filaments of lengths ranging from ∼400 nm to 14 nm were prepared by assembling actin in the presence of gelsolin and calcium (G = gelsolin, A = Actin). As the length of the actin filament becomes limiting, FLNa molecules attach only with one of their ABDs, P < 0.0001 (t test; n = 11–45).