ARA induction of tau isoform polymerization. 2 μM tau isoforms were incubated with various ARA concentrations (0 μM to 100 μM) for 18 hrs. Polymerization was measured by (A) LLS or (B) ThS fluorescence. Symbols correspond as follows: (open square) 0N3R, (closed square) 0N4R, (open triangle) 1N3R, (closed triangle) 1N4R, (open circle) 2N3R, (closed circle) 2N4R, and (closed diamond) assembly incompetent protein (AIP (I277, 308P)). Data is in arbitrary units and represents an average of 3 trials ± SEM. After 18 hours, ARA induced polymerization reactions were visualized by TEM at 20,000x magnification. Images are as follows: (C) 0N3R, (D) 1N3R, (E) 2N3R, (F) 0N4R, (G) 1N4R, and (H) 2N4R. Each isoform image is representative of polymerized material at 75 μM ARA. Scale bars represent 1 μm.