<p>Supplemental Figure 1.</p><p>(A) Specific reactivity of HSP70, HSP90, and 14–3–3 antisera. Antisera against 14–3– 3, HSP70, and HSP90 recognized the purified protein as well as the endogenous proteins in wheat germ lysate specifically, whereas corresponding preimmunsera of the tested antibodies do not show any unspecific interaction with the proteins or the wheat germ lysate.</p><p>(B) 14–3–3, HSP90, and HSP70 are specific for cytosolic chaperones. Wheat chloroplasts (15 g of chlorophyll) and wheat germ lysate was probed with antisera against 14–3–3, HSP90, HSP70, and LHCII (light-harvesting complex II), which is only present in the chloroplasts.</p><p>(C) Co-immunoprecipitations showing simultaneous binding of HSP70 and HSP90 or 14–3–3. Figures correspond to co-immunoprecipitations in Figure 1.</p><p>(D) Authentic proteins used for the chimeric constructs in Figure 2 bind to HSP70.</p><p>(E) WG and reticulocyte lysate (1 l each) were probed with HSP90 antisera.</p><p>(F) HSP70 is precipitated specifically with HSP70 antisera and not with PS from wheat germ lysate.</p><p>(G) pDSP4 and pRPL28 were precipitated successfully with HSP70 antisera after incubation for 15 min with protein A sepharose.</p><p>Supplemental Figure 2. Postribosomal Supernatants of Translated pNFU2, pSSU, pNdhM, pLHCA5, and pHCF101 Were Fractionated by Size Exclusion Chromatography.</p><p>The obtained fractions (1–12) were precipitated with TCA and separated on SDS– PAGE. In contrast to pNFU2 (upper panel), the 14–3–3 binding proteins (pSSU and pNdhM, middle panel) accumulate at a lower molecular weight. pLHCA5 and pHCF101 (lower panels), which were only found to be associated with HSP70 (Figure 1C), did not show a distinct elution pattern.</p><p>Supplemental Figure 3. Mass Spectrometric Analysis Corresponding to Matching Peptides from Figure 4A.</p><p>Sequences were blasted against all plant databases. Supplemental Figure 4. Protein Alignment of TaHOP with HOP Proteins from Other Species.</p><p>Arabidopsis thaliana (AtHOP-1, AtHOP-2, AtHOP-3), Glycine max (GmHOP), Homo sapiens (HsHOP), and Saccharomyces cerevisiae (ScHOP). Predicted TPR regions are marked in gray.</p>