title: Trigger Factor can antagonize both SecB and DnaK/DnaJ chaperone functions in Escherichia coli.
abstract: Polypeptides emerging from the ribosome are assisted by a pool of molecular chaperones and targeting factors, which enable them to efficiently partition as cytoplasmic, integral membrane, or exported proteins. In Escherichia coli, the chaperones SecB, Trigger Factor (TF), and DnaK are key players in this process. Here, we report that, as with dnaK or dnaJ mutants, a secB null strain exhibits a strong cold-sensitive (Cs) phenotype. Through suppressor analyses, we found that inactivating mutations in the tig gene encoding TF fully relieve both the Cs phenotype and protein aggregation observed in the absence of SecB. This antagonistic effect of TF depends on its ribosome-binding and chaperone activities but unrelated to its peptidyl-prolyl cis/trans isomerase (PPIase) activity. Furthermore, in contrast to the previously known synergistic action of TF and DnaK/DnaJ above 30 degrees C, a tig null mutation partially suppresses the Cs phenotype exhibited by a compromised DnaK/DnaJ chaperone machine. The antagonistic role of TF is further exemplified by the fact that the secB dnaJ double mutant is viable only in the absence of TF. Finally, we show that, in the absence of TF, more SecA and ribosomes are associated with the inner membrane, suggesting that the presence of TF directly or indirectly interferes with the process of cotranslational protein targeting to the Sec translocon.
authors.affiliation: Département de Microbiologie et Médecine Moléculaire, Centre Médical Universitaire, 1 Rue Michel-Servet, CH-1211 Geneva, Switzerland.
authors.forename: Ronald S
authors.initials: RS
authors.lastname: Ullers
authors.forename: Debbie
authors.initials: D
authors.lastname: Ang
authors.forename: Françoise
authors.initials: F
authors.lastname: Schwager
authors.forename: Costa
authors.initials: C
authors.lastname: Georgopoulos
authors.forename: Pierre
authors.initials: P
authors.lastname: Genevaux
mesh_terms: D001426:Bacterial Proteins / Q000037:antagonists & inhibitors* / Q000235:genetics; D002462:Cell Membrane / Q000378:metabolism; D003080:Cold Temperature; D004591:Electrophoresis, Polyacrylamide Gel; D004926:Escherichia coli / Q000254:growth & development / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism*; D017353:Gene Deletion; D050956:HSP40 Heat-Shock Proteins / Q000037:antagonists & inhibitors*; D018840:HSP70 Heat-Shock Proteins / Q000037:antagonists & inhibitors*; D018832:Molecular Chaperones / Q000378:metabolism*; D009154:Mutation / Q000235:genetics; D019696:Peptidylprolyl Isomerase / Q000235:genetics / Q000378:metabolism*; D010641:Phenotype; D012270:Ribosomes / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; C494635:DnaJ protein, E coli; D029968:Escherichia coli Proteins; D050956:HSP40 Heat-Shock Proteins; D018840:HSP70 Heat-Shock Proteins; D018832:Molecular Chaperones; C057842:SecB protein, Bacteria; C063842:dnaK protein, E coli; C403324:trigger factor, E coli; D019696:Peptidylprolyl Isomerase