title: The "trigger factor cycle" includes ribosomes, presecretory proteins, and the plasma membrane.
abstract: Trigger factor is a soluble, 63,000 dalton protein of E. coli that stabilizes proOmpA, the precursor form of a major outer-membrane protein, in a conformation competent for in vitro membrane assembly. There is approximately one trigger factor molecule bound to each 70S ribosome isolated from cell extracts in physiological buffers. Trigger factor dissociates from ribosomes in 1.5 M LiCl and reassociates with salt-washed ribosomes in low-salt buffer. Binding is exclusively to the 50S (large) subunit, known to contain the exit domain for nascent polypeptide chains. In addition to its associations with proOmpA and ribosomes, excess trigger factor can compete with the proOmpA-trigger factor complex for a limited number of membrane sites that are essential for translocation of proOmpA. These data suggest a model of trigger factor cycling between the cytoplasm, the ribosome, presecretory proteins, and membrane receptor proteins.
mesh_terms: D000591:Amino Acid Isomerases / Q000302:isolation & purification / Q000378:metabolism*; D001425:Bacterial Outer Membrane Proteins / Q000378:metabolism; D001426:Bacterial Proteins / Q000302:isolation & purification / Q000378:metabolism*; D001692:Biological Transport; D002352:Carrier Proteins / Q000302:isolation & purification / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism*; D002499:Centrifugation, Density Gradient; D004926:Escherichia coli / Q000378:metabolism; D029968:Escherichia coli Proteins; D008954:Models, Biological; D008970:Molecular Weight; D019696:Peptidylprolyl Isomerase; D011498:Protein Precursors / Q000378:metabolism; D012269:Ribosomal Proteins / Q000302:isolation & purification / Q000378:metabolism*; D012270:Ribosomes / Q000378:metabolism*
chemical_list: D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D002352:Carrier Proteins; D029968:Escherichia coli Proteins; D011498:Protein Precursors; D012269:Ribosomal Proteins; C057184:outer membrane protein A precursor (E coli); D000591:Amino Acid Isomerases; D019696:Peptidylprolyl Isomerase