Figure 1.

Working model of cytosolic phosphorylation of chloroplast transit peptides. The cytosolic kinases are phosphorylated by an intramolecular event resulting in active kinase molecules, which can subsequently phosphorylate chloroplast transit peptides on serine and threonine residues. Phosphorylation and 14-3-3 binding enhances association with the Toc receptor, from where the proteins are imported after dephosphorylation by an as yet unidentified protein phosphatase.