Figure 1.

Schematic diagram of Toc159-actin interactions and the import of photosynthesis proteins. Toc159, linked to actin by its A-domain, recruits a newly synthesized photosynthesis preprotein by its G-domain. Actin filaments facilitate Toc159 movement to the chloroplast outer envelope membrane for integration into the TOC complex. The core TOC complex is formed by Toc159, Toc34 and Toc75. Tic22 acts to facilitate the passage of preproteins across the intermembrane space and interacts with the TIC complex. The core TIC complex is composed of Tic110, Tic20 and/or Tic21, and Tic40. The Tic110 protein recruits stromal molecular chaperone ClpC. On arrival in the stroma, the transit peptide is cleaved by SPP, and other chaperones (Hsp90 or Hsp70) may assist in the folding. VIPP1 interacts with the chaperones and polymerises, inducing chloroplast inner envelope membrane budding, leading to thylakoid formation.