Figure 2

Comparison of the chloroplast target peptides of red algae and heterokonts. part A: To be imported into a red algal chloroplast, proteins require only a single N-terminal transit peptide (blue bar). The transit peptide is cleaved when the protein passes through the outer chloroplast membrane. The mature protein (yellow) is then transferred into the chloroplast. part B: In heterokonts, proteins which are targeted to the chloroplast possess a bipartite target peptide which is made up of an N-terminal signal peptide (red) followed by a chloroplast transit peptide (blue). The signal peptide is cleaved when the protein passes through the outermost of the four heterokont chloroplast membranes. This places the transit peptide at the new N-terminus of the protein where it can mediate transfer across the two innermost membranes. The transit peptide is cleaved during this second step of the transfer. part C: Sequence logo of the conserved ASAFAP motif surrounding the predicted signal peptide cleavage site based on 55 chloroplast targeted proteins from heterokonts. The logo was built with WebLogo [53] and is based on manually improved alignments of the sequence neighbouring the predicted cleavage site.