SecB functions as a cytosolic signal recognition factor for protein export in E. coli.
A purified 64 kd protein, consisting of four identical subunits of the 16 kd SecB, binds to the signal sequence of preproteins prior to their translocation across inverted vesicles (INV) derived from the E. coli plasma membrane. The purified SecB tetramer competes with canine signal recognition particle (SRP) in signal sequence binding and thus behaves as a prokaryotic equivalent of SRP. As shown by cell fractionation and immunoblot analysis with anti-SecB antibodies, SecB is a cytosolic protein. An E. coli supernatant depleted of SecB after passage through an anti-SecB Sepharose column retains full translation activity but is unable to support translocation into added INV. Translocation into INV is fully restored by readdition of purified SecB.
Watanabe
M
M
Laboratory of Cell Biology, Howard Hughes Medical Institute, Rockefeller University, New York, New York 10021.
Blobel
G
G
D001426:Bacterial Proteins / Q000378:metabolism*; D001692:Biological Transport; D003600:Cytosol / Q000378:metabolism; D004926:Escherichia coli / Q000502:physiology*; D007158:Immunologic Techniques; D066298:In Vitro Techniques; D011485:Protein Binding; D011498:Protein Precursors / Q000378:metabolism; D021382:Protein Sorting Signals / Q000378:metabolism; D012261:Ribonucleoproteins / Q000502:physiology*; D018271:Signal Recognition Particle
D001426:Bacterial Proteins; D011498:Protein Precursors; D021382:Protein Sorting Signals; D012261:Ribonucleoproteins; D018271:Signal Recognition Particle