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Updated: Aug 4, 2026

Isolation of Physiologically Active Thylakoids and Their Use in Energy-Dependent Protein Transport Assays
Published on: September 28, 2018
SecYEG and SecA are the stoichiometric components of preprotein translocase
K Douville1, A Price, J Eichler
1Department of Biochemistry, Dartmouth Medical School, Hanover, New Hampshire 03755-3844, USA.
Abstract:
The transport of large preproteins across the Escherichia coli plasma membrane is catalyzed by preprotein translocase, comprised of the peripherally bound SecA subunit and an integrally bound heterotrimeric domain consisting of the SecY, SecE, and SecG subunits. We have now placed the secY, secE, and secG genes under the control of an arabinose-inducible promoter on a multicopy plasmid. Upon induction, all three of the proteins are strongly overexpressed and recovered in the plasma membrane fraction. These membranes show a strong enhancement of 1) translocation ATPase activity, 2) preprotein translocation, 3) capacity for SecA binding, and 4) formation of the membrane-inserted form of SecA. These data establish that SecY, SecE, and SecG constitute the integral membrane domain of preprotein translocase.
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