Fig. 1. Targeting and sorting signals of mitochondrial proteins. N-terminal cleavable presequences are shown in light green, transmembrane segments in purple. Sorting signals to the IMS (the intermembrane space) of IM (inner membrane) consist of a hydrophobic segment (purple) flanked by hydrophilic segments (dark blue). Cleavage sites are indicated by arrowheads. From the top to the bottom, precursor proteins with a presequence that are targeted to the matrix or inserted into the IM from the matrix side, IM proteins with a presequence that are anchored to the IM by a single transmembrane segment with the N_in-C_out orientation (e.g. D-lactate dehydrogenase and subunit Va of cytochrome c oxidase), precursor proteins with a bipartite presequence containing a sorting signal to the IMS (e.g. cytochrome b₂ and cytochrome c₁), and polytopic IM proteins without a presequence (e.g. AAC) are shown. + indicates positively charged regions.