PMID:2649892
| Citation |
Watanabe, M and Blobel, G (1989) Cytosolic factor purified from Escherichia coli is necessary and sufficient for the export of a preprotein and is a homotetramer of SecB. Proc. Natl. Acad. Sci. U.S.A. 86:2728-32 |
|---|---|
| Abstract |
We have purified to homogeneity a cytosolic factor from Escherichia coli that is required for the translocation of a preprotein into inverted vesicles of the E. coli plasma membrane. The preprotein used is a precursor of mutant maltose-binding protein. This mutant contains alterations of the carboxyl terminus. Unlike the precursor for wild-type maltose-binding protein, the mutant precursor does not acquire a protease-resistant conformation after synthesis and retains posttranslational translocation competence. The purified cytosolic factor, added posttranslationally, is necessary and sufficient to yield virtually 100% translocation of the mutant precursor into inverted vesicles. The purified factor amounts to 0.08% of the cytosolic proteins and is a 64-kDa tetramer consisting of four identical 16-kDa subunits. Amino-terminal sequence analysis revealed that it is identical to the secB gene product. The purified SecB homotetramer is part of a larger 150-kDa complex that represents the "export" factor activity. During purification, the export factor activity dissociates into a 64-kDa SecB homotetramer and unidentified component(s). For the posttranslational integration of another preprotein, the precursor for the lamB gene product, into inverted vesicles, the 64-kDa SecB homotetramer is also required but additional factor(s) makes integration more efficient. |
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| Keywords |
ATP-Binding Cassette Transporters; Amino Acid Sequence; Bacterial Proteins/isolation & purification; Bacterial Proteins/physiology; Carrier Proteins/secretion; Chromatography; Cytosol/analysis; Escherichia coli/analysis; Escherichia coli/physiology; Escherichia coli Proteins; Genes, Bacterial; Maltose-Binding Proteins; Molecular Sequence Data; Molecular Weight; Monosaccharide Transport Proteins; Protein Processing, Post-Translational |
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