Science 338 (6107): 622-623
Copyright © 2012 by the American Association for the Advancement of Science
Chloroplast Delivery by UPS
Institute of Biology, University of Neuchâtel, CH-2000 Neuchâtel, Switzerland.
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Model of chloroplast biogenesis. Nonphotosynthetic, undifferentiated plastids in the dark (etioplasts) import housekeeping proteins via a translocon at the outer membrane of the chloroplast (Toc) complex consisting of the preprotein receptors Toc132/-120 and Toc34 together with the protein-translocating channel Toc75. Light triggers the transformation of etioplasts into chloroplasts. Developing chloroplasts import large quantities of photosynthesis-associated proteins using a Toc complex consisting of the preprotein receptors Toc159 and Toc33 together with Toc75. The remodeling of the Toc complex during chloroplast biogenesis implicates an outer membrane E3 ligase, SP1, that targets components of the protein import machinery for degradation by the 26S proteasome (26SP). A, acidic; at, Arabidopis thaliana; G, GTP-binding; M, membrane insertion; RNF, RING-finger domain; Ub, ubiquitin.|