Trigger factor retards protein export in Escherichia coli.
Trigger factor (TF) is a ribosome-associated protein that interacts with a wide variety of nascent polypeptides in Escherichia coli. Previous studies have indicated that TF cooperates with DnaK to facilitate protein folding, but the basis of this cooperation is unclear. In this study we monitored protein export in E. coli that lack or overproduce TF to obtain further insights into its function. Whereas inactivation of genes encoding most molecular chaperones (including dnaK) impairs protein export, inactivation of the TF gene accelerated protein export and suppressed the need for targeting factors to maintain the translocation competence of presecretory proteins. Furthermore, overproduction of TF (but not DnaK) markedly retarded protein export. Manipulation of TF levels produced similar effects on the export of a cytosolic enzyme fused to a signal peptide. The data strongly suggest that TF has a unique ability to sequester nascent polypeptides for a relatively prolonged period. Based on our results, we propose that TF and DnaK promote protein folding by distinct (but complementary) mechanisms.
Lee
Hin C
HC
Genetics and Biochemistry Branch, NIDDK, National Institutes of Health, Bethesda, Maryland 20892, USA.
Bernstein
Harris D
HD
D001483:Base Sequence; D003001:Cloning, Molecular; D017931:DNA Primers; D004926:Escherichia coli / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000378:metabolism*; D007700:Kinetics; D008954:Models, Biological; D010455:Peptides / Q000378:metabolism; D019696:Peptidylprolyl Isomerase / Q000378:metabolism*; D010957:Plasmids; D016133:Polymerase Chain Reaction; D021381:Protein Transport; D011994:Recombinant Proteins / Q000378:metabolism; D012269:Ribosomal Proteins / Q000378:metabolism
D017931:DNA Primers; D029968:Escherichia coli Proteins; D010455:Peptides; D011994:Recombinant Proteins; D012269:Ribosomal Proteins; C403324:trigger factor, E coli; D019696:Peptidylprolyl Isomerase