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Microbiol. Rev., Sep 1996, 512-538, Vol 60, No. 3
SC Makrides
Progress in our understanding of several biological processes promises to
broaden the usefulness of Escherichia coli as a tool for gene expression.
There is an expanding choice of tightly regulated prokaryotic promoters
suitable for achieving high-level gene expression. New host strains
facilitate the formation of disulfide bonds in the reducing environment of
the cytoplasm and offer higher protein yields by minimizing proteolytic
degradation. Insights into the process of protein translocation across the
bacterial membranes may eventually make it possible to achieve robust
secretion of specific proteins into the culture medium. Studies involving
molecular chaperones have shown that in specific cases, chaperones can be
very effective for improved protein folding, solubility, and membrane
transport. Negative results derived from such studies are also instructive
in formulating different strategies. The remarkable increase in the
availability of fusion partners offers a wide range of tools for improved
protein folding, solubility, protection from proteases, yield, and
secretion into the culture medium, as well as for detection and
purification of recombinant proteins. Codon usage is known to present a
potential impediment to high-level gene expression in E. coli. Although we
still do not understand all the rules governing this phenomenon, it is
apparent that "rare" codons, depending on their frequency and context, can
have an adverse effect on protein levels. Usually, this problem can be
alleviated by modification of the relevant codons or by coexpression of the
cognate tRNA genes. Finally, the elucidation of specific determinants of
protein degradation, a plethora of protease-deficient host strains, and
methods to stabilize proteins afford new strategies to minimize proteolytic
susceptibility of recombinant proteins in E. coli.
Copyright © 1996, American Society for Microbiology
Strategies for achieving high-level expression of genes in Escherichia coli
Department of Molecular Biology, T Cell Sciences, Inc., Needham, Massachusetts 02194, USA.
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