Fig. 2: Septin filaments align laterally and longitudinally on yeast polar supported lipid bilayers.

a HS-AFM movie frame, and b magnified view of the dashed outlined region in (a) (49 frame time average), of septin filaments on a yeast polar lipid SLB in buffer, 20 mM HEPES, pH 6, 50 mM KCl. c Example section profiles along the two filaments in the region of the dashed outline in (b). The red and black traces correspond to the filaments indicated by the red and the black arrowheads in (b). d Cross correlation value vs phase-lag plot of the two traces shown in (c) as they are computationally phase shifted from −180° to +180° with respect to each other, peaking at a phase-lag φ = 0° with a cross-correlation value of 0.82. e Histogram distribution of filament neighbor alignment phase lag, φ, for each set of rods in neighboring filament pairs, peaking at 0° with a full width at half maximum (FWHM) of 21° (n = 170 filament rod neighbors). Note the distribution is symmetric because the septin filaments are palindromic and have therefore no directionality with respect to nearest neighbors. The signal-to-noise ratio was sufficient to observe longitudinal periodicity in 9 HS-AFM movies from 5 biological replicates.