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Translocon at the Outer-envelope membrane of Chloroplasts 34-like (Toc34-like) The Toc34-like (Translocon at the Outer-envelope membrane of Chloroplasts) family contains several Toc proteins, including Toc34, Toc33, Toc120, Toc159, Toc86, Toc125, and Toc90. The Toc complex at the outer envelope membrane of chloroplasts is a molecular machine of ~500 kDa that contains a single Toc159 protein, four Toc75 molecules, and four or five copies of Toc34. Toc64 and Toc12 are associated with the translocon, but do not appear to be part of the core complex. The Toc translocon initiates the import of nuclear-encoded preproteins from the cytosol into the organelle. Toc34 and Toc159 are both GTPases, while Toc75 is a beta-barrel integral membrane protein. Toc159 is equally distributed between a soluble cytoplasmic form and a membrane-inserted form, suggesting that assembly of the Toc complex is dynamic. Toc34 and Toc75 act sequentially to mediate docking and insertion of Toc159 resulting in assembly of the functional translocon.
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