MAC composition and actin pattern formation by myofilaments. (A) Scheme of the MAC. Biotinylated actin filaments are coupled to a supported lipid bilayer (Egg PC) containing biotinylated lipids (DSPE-PEG(2000)-Biotin) via Neutravidin. (B) TIRFM images of MACs containing Alexa-488-phalloidin labeled actin filaments. The increase of actin filament densities (left to right) corresponds to an increase in the amount of DSPE-PEG200-Biotin (low = 0.01 mol%, medium = 0.1 mol%, high = 1 mol%) in the membrane. Scale bars, 10 µm. (C) Length distribution of myofilaments. The median length (Lm) and the 25th and 75th percentile (brackets) are indicated in µm. Inset shows a topographical AFM image of a myofilament. Height, 12 nm; scale bar 200 nm. (D) Dual-color TIRFM time-lapse images of a medium actin density MAC with Alexa-488-phalloidin labeled actin filaments (green) and myofilaments (0.3 µM unlabeled myosin II doped with Alexa 647 myosin II (red)) before (left image) and during actin pattern formation. Scale bars, 10 µm.