Membrane insertion of the chloroplast outer envelope protein, Toc34: constrains for insertion and topology.

The insertion of the outer envelope protein Toc34 from chloroplasts was studied. Toc34 was chosen as a model protein because it contains one predicted transmembrane helix at the C-terminus and a large hydrophilic N-terminal located GTPase domain, which is exposed to the cytosol. Unlike proteins located in internal chloroplast compartments, Toc34 neither contains a cleavable presequence nor uses the general import pathway.