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Published May 7, 2010 | Supplemental Material + Accepted Version
Journal Article Open

Sequential Checkpoints Govern Substrate Selection During Cotranslational Protein Targeting


Proper protein localization is essential for all cells. However, the precise mechanism by which high fidelity is achieved is not well understood for any protein-targeting pathway. To address this fundamental question, we investigated the signal recognition particle (SRP) pathway in Escherichia coli, which delivers proteins to the bacterial inner membrane through recognition of signal sequences on cargo proteins. Fidelity was thought to arise from the inability of SRP to bind strongly to incorrect cargos. Using biophysical assays, we found that incorrect cargos were also rejected through a series of checkpoints during subsequent steps of targeting. Thus, high fidelity of substrate selection is achieved through the cumulative effect of multiple checkpoints; this principle may be generally applicable to other pathways involving selective signal recognition.

Additional Information

© 2010 American Association for the Advancement of Science. Received 6 January 2010; accepted 18 March 2010. We thank C. Schaffitzel and N. Ban for help with the purification of RNCs and Trigger factor; J. Luirink for plasmids encoding the phoA signal sequence variants; L. Randall for the plasmid encoding luciferase; B. Bukau and E. Deuerling for the plasmid encoding Trigger factor; F. Nataro for the plasmid encoding EspP; H. D. Bernstein for the strain HDB51; and R. J. Deshaies, A. Varshavsky, W. Zhong, N. Pierce, and the Shan laboratory for comments on the manuscript. This work was supported by NIH grant GM078024, and career awards from the Burroughs Wellcome Foundation, the Henry and Camille Dreyfus Foundation, the Arnold and Mabel Beckman Foundation, and the Packard Foundation to S.S.

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Accepted Version - nihms505487.pdf

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