Figure 6. Model of translocon complex assembly states during precursor import into chloroplasts.

During import, precursors first associate with the C1 complex composed of the Toc components. A population of C1 may contain Toc159 in a different conformation. Another distinct complex, C2, composed of the Toc components, Tic110, Hsp93, and hsp70 exists. However, whether C2 is an intermediate step between C1 and the Tic/Toc supercomplex is not clear. The presence of Tic22 and Tic20 in C2 has also not yet been demonstrated. Other additional translocon components, like Tic40, then assemble to form the Tic/Toc supercomplex. The scissor represents the stromal transit-peptide processing peptidase and its position indicates that processing most likely occurs at the supercomplex.