title: Multicopy suppression of cold-sensitive sec mutations in Escherichia coli.
abstract: 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.
authors.affiliation: Department of Molecular Biology, Princeton University, New Jersey 08544-1014, USA.
authors.forename: P N
authors.initials: PN
authors.lastname: Danese
authors.forename: C K
authors.initials: CK
authors.lastname: Murphy
authors.forename: T J
authors.initials: TJ
authors.lastname: Silhavy
mesh_terms: D001426:Bacterial Proteins / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism; D001483:Base Sequence; D001692:Biological Transport; D018835:Chaperonin 10 / Q000096:biosynthesis / Q000235:genetics; D018834:Chaperonin 60 / Q000096:biosynthesis / Q000235:genetics; D004926:Escherichia coli / Q000235:genetics*; D029968:Escherichia coli Proteins; D018628:Gene Dosage; D005822:Genetic Vectors; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D008969:Molecular Sequence Data; D016296:Mutagenesis / Q000235:genetics*; D010957:Plasmids / Q000235:genetics; D017384:Sequence Deletion; D013489:Suppression, Genetic; D001616:beta-Galactosidase / Q000096:biosynthesis / Q000235:genetics
chemical_list: D001426:Bacterial Proteins; D018835:Chaperonin 10; D018834:Chaperonin 60; D029968:Escherichia coli Proteins; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; C499394:SecD protein, E coli; C489583:SecF protein, E coli; C075767:secD protein, Bacteria; C075768:secF protein, Bacteria; D001616:beta-Galactosidase