Rocket Launcher Mechanism of Collaborative Actin Assembly Defined by Single-Molecule Imaging

See How They Grow Controlled assembly and disassembly of the actin cytoskeleton is essential for processes such as cell motility, cytokinesis, and tumor metastasis. The formation of new actin filaments appears to involve the protein formin paired with another actin assembly-promoting factor. Breitsprecher et al. (p. 1164 ) used triplecolor single-molecule fluorescence microscopy to visualize actin assembly promoted by the formin, mDia1, and the tumor-suppressor, adenomatous polyposis coli (APC). The two assembly factors interacted directly to initiate filament assembly, after which mDia1 moved with the growing barbed ends while APC remained at the site of nucleation.