FIGURE 8.

At-cpSRP54M is required for the formation of low molecular weight transit complexes in Arabidopsis. To analyze the ability of cpSRP components to form soluble complexes with LHCP, the following combinations of recombinant proteins were used, and protein mixtures were separated by size exclusion chromatography: At-His-cpSRP43 (43), LHCP, and At-His-cpSRP54MΔ530–564 (54MΔC) (A); At-His-cpSRP43 and LHCP (B); and At-His-cpSRP43, At-His-cpSRP54M (54M), and LHCP (C). As controls, the combination of At-His-cpSRP43 and At-His-cpSRP54M (D) and the single proteins At-His-cpSRP43 (E) and At-His-cpSRP54M (F) were analyzed. The single proteins were treated in the same way as in assays analyzing complex formation. As At-cpSRP54M has a very low absorbance at 280 nm, the chromatogram is not shown. Elution fractions ranging from 8 to 18.5 ml were analyzed by SDS-PAGE and Coomassie staining (A, B, D, E, and F) or Western blotting (C) to distinguish between LHCP and At-His-cpSRP54M as both proteins have the same running behavior in SDS-PAGE. The complex formation assays shown in A, B, and D contained equimolar amounts of the indicated recombinant proteins, whereas in the assay shown in C At-His-cpSRP54M, At-His-cpSRP43, and LHCP were incubated at a molar ratio of 1:2:2. mAU, milliabsorbance units.