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J. Bacteriol., 09 1995, 4969-4973, Vol 177, No. 17
PN Danese, CK Murphy and TJ Silhavy
Mutations in the secretory (sec) genes in Escherichia coli compromise
protein translocation across the inner membrane and often confer
conditional-lethal phenotypes. We have found that overproduction of the
chaperonins GroES and GroEL from a multicopy plasmid suppresses a wide
array of cold-sensitive sec mutations in E. coli. Suppression is
accompanied by a stimulation of precursor protein translocation. This
multicopy suppression does not bypass the Sec pathway because a deletion of
secE is not suppressed under these conditions. Surprisingly, progressive
deletion of the groE operon does not completely abolish the ability to
suppress, indicating that the multicopy suppression of cold-sensitive sec
mutations is not dependent on a functional groE operon. Indeed,
overproduction of proteins unrelated to the process of protein export
suppresses the secE501 cold- sensitive mutation, suggesting that protein
overproduction, in and of itself, can confer mutations which compromise
protein synthesis and the observation that low levels of protein synthesis
inhibitors can suppress as well. In all cases, the mechanism of suppression
is unrelated to the process of protein export. We suggest that the
multicopy plasmids also suppress the sec mutations by compromising protein
synthesis.
Copyright © 1995, American Society for Microbiology
Multicopy suppression of cold-sensitive sec mutations in Escherichia coli
Department of Molecular Biology, Princeton University, New Jersey 08544- 1014, USA.
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