Isolated outer chloroplast envelope membranes were solubilized by digitonin and separated on linear sucrose density gradients. A membrane complex was recovered from the gradients and exhibited characteristics of a protein import apparatus, i.e. the interaction of the complex with the precursor polypeptides depends on the presence of a transit sequence, ATP and protease‐sensitive components. Furthermore, trans‐location intermediates detected in the organellar system are also found after interaction of the precursor polypeptide with the isolated import complex.
. 1993. The protein Import apparatus of chloroplash. -Ph,sinl Plant. X7: 433--440. Routing of cyt050lically synthesized precursor proteins into chloroplasts is a specific process which involves a multitudc of soluhle and memhrane components. In this review we will focus on early events of the translocation pathway of nuclear coded plastidic precursor proteins and compare import routes fll[ polypeptides of the outer chloroplast envelope to that of internal chloroplast compartments. A numher of proteins housed in the chloroplast enYelopes have heen implied to ne involv'cd in the translocation process. but so far a certain function has not been a~signcd to any of these protems. The only exception could be an envelope localized hsc 70 homologue which could retain the import competence of Cl prccu"or protein in transit inlO the organelle.K(r words -Chloroplasts. envelope mcmhrancs. import app
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