FIGURE 3.

Principle of the tethered particle method. (A) A microsphere (shown in pink) is tethered at the 3′ end of an mRNA molecule, which is bound to a ribosome immobilized on a microscope slide. The mRNA molecule is shown as a curvy black line, the end-to-end length of the tether is shown as a black dotted line, and the peptide synthesized by the ribosome is shown in orange. The microsphere can diffuse only within the range limited by the surface of the slide and the length of the tether, as shown by the green dashed line and shading. (B) As peptide synthesis proceeds, the ribosome pulls the 3′ end of the mRNA toward itself, reducing the range of restricted diffusion (schematic not drawn to scale).