FIGURE 1.

Schematic of magnetocapture assay. (A) Radiolabeled PRNA (gray, helical) and P protein (black, with His-tag labeled H) are incubated to form equilibrium concentrations of free PRNA, free P protein, and holoenzyme complex. (B) Magnetic agarose Ni-NTA beads are added to bind the free P protein and the holoenzyme complex. (C) An external magnetic strip is applied to pull the magnetic beads with the bound holoenzyme complex and noncomplexed His-tagged P protein from the bulk solution where the free PRNA is located. (D) The free radiolabeled PRNA is removed in the wash and counted in a scintillation counter. (E) The bound complexes and proteins are removed from the beads and quantitated by Cerenkov scintillation counting.