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J. Bacteriol., 03 1995, 1497-1504, Vol 177, No. 6
H Dong, L Nilsson and CG Kurland
We attempted to test the idea that the relative abundance of each
individual tRNA isoacceptor in Escherichia coli can be altered by varying
its cognate codon concentration. In order to change the overall codon
composition of the messenger pool, we have expressed in E. coli lacZ with
the aid of T7 RNA polymerase so that their respective gene products
individually accounted for 30% of the total bacterial protein.
Unexpectedly, the maximum expression of either test gene has no specific
effect on the relative rates of synthesis of the tRNA species that we
studied. Instead, we find that there is a cumulative breakdown of rRNAs,
which results in a loss of ribosomes and protein synthetic capacity. After
either of the test genes is maximally induced, there is a growing fraction
of protein synthesis invested in beta-galactosidase or delta tufB that is
matched by a comparable decrease of the fraction of normal protein
synthesis. We have also observed enhanced accumulation of two heat shock
proteins during overexpression. Finally, after several hours of
overexpression of either test protein, the bacteria are no longer viable.
These results are relevant to the practical problems of obtaining high
expression levels for cloned proteins.
Copyright © 1995, American Society for Microbiology
Gratuitous overexpression of genes in Escherichia coli leads to growth inhibition and ribosome destruction
Department of Molecular Biology, Biomedical Centrum, Uppsala, Sweden.
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