Cytosolic factor purified from Escherichia coli is necessary and sufficient for the export of a preprotein and is a homotetramer of SecB.
- 1 April 1989
- journal article
- research article
- Published by Proceedings of the National Academy of Sciences in Proceedings of the National Academy of Sciences
- Vol. 86 (8) , 2728-2732
- https://doi.org/10.1073/pnas.86.8.2728
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.This publication has 13 references indexed in Scilit:
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