title: Identification of a soluble SecA/SecB complex by means of a subfractionated cell-free export system.
abstract: We have reconstituted the cell-free synthesis of the Escherichia coli precursor protein LamB from partially purified subfractions of an E. coli cell extract. PreLamB synthesized in this manner is translocated into salt-extracted plasma membrane vesicles only in the presence of SecA/SecB- or SecB-containing preparations of the E. coli cytosol. The most active preparations obtained upon purification were those containing a soluble SecA/SecB complex. Complex formation between SecA and SecB was verified by co-sedimentation and co-immunoprecipitation. When preLamB was synthesized in the presence of this material, a considerable amount of precursor was recovered from a soluble ternary complex consisting of preLamB, SecA, and SecB. Our results suggest that a soluble SecA/SecB complex participates in the export of preLamB and that this complex is functionally equivalent to a previously described 12 S (7 S) export factor (Müller, M., and Blobel, G. (1984) Proc. Natl. Acad. Sci. U.S.A. 81, 7737-7741; Watanabe, M., and Blobel, G. (1989) Proc. Natl. Acad. Sci. U.S.A. 86, 2728-2732).
authors.affiliation: Institut für Physikalische Biochemie, Universität München, Germany.
authors.forename: H K
authors.initials: HK
authors.lastname: Hoffschulte
authors.forename: B
authors.initials: B
authors.lastname: Drees
authors.forename: M
authors.initials: M
authors.lastname: Müller
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism*; D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins / Q000378:metabolism*; D001692:Biological Transport; D002458:Cell Fractionation; D002462:Cell Membrane / Q000378:metabolism; D002474:Cell-Free System; D003600:Cytosol / Q000378:metabolism; D004926:Escherichia coli / Q000378:metabolism; D029968:Escherichia coli Proteins; D026901:Membrane Transport Proteins; D018272:Porins; D011498:Protein Precursors / Q000378:metabolism; D011991:Receptors, Virus / Q000378:metabolism; D000069816:SEC Translocation Channels; D000081416:SecA Proteins
chemical_list: D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D026901:Membrane Transport Proteins; D018272:Porins; D011498:Protein Precursors; D011991:Receptors, Virus; D000069816:SEC Translocation Channels; C057842:SecB protein, Bacteria; C016532:maltoporins; D000251:Adenosine Triphosphatases; D000081416:SecA Proteins