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. 2011 Dec 6;287(4):2446–2458. doi: 10.1074/jbc.M111.292748

FIGURE 1.

FIGURE 1.

High resolution AFM imaging reveals mRNA assembly into granules and MT bundling under macromolecular crowding environment. A, at moderate ionic strength (20 mm Tris-HCl, pH 7.4, 50 mm KCl), 1% PEG 35K (w/v), a crowding agent, triggers the assembly of MTs into thick bundles, and 20% PEG 35K triggers that of 2Luc mRNA into granules. In contrast, PEG 1K was unable to induce mRNA self-assembly, as expected for excluded volume interactions because of its small size. Incubation time, 30 min. Scale bars, 2.5 μm (AFM images of MTs) and 1 μm (AFM images of mRNAs). B, with 0.5 and 15% PEG 35K at moderate ionic strength, no MT bundles or mRNA aggregates were detected, respectively. However, increasing KCl concentration led to the progressive appearance of MT bundles or mRNA granules. When betaine, a neutral osmolyte, was used instead of KCl to increase the osmolality without increasing the ionic strength, no mRNA granules or MT bundles were observed. Incubation time, 30 min. Scale bars, 2.5 μm (AFM images of MTs) and 1 μm (AFM image of mRNAs).