E. coli trigger factor is an abundant cytosolic protein originally iDAntified by its ability to maintain the precursor of a secretory protein in a translocation competent form. Recent studies shed new light on the function of this protein. Trigger factor was found to be a peptidyl-prolyl-cisltrans-isomerase capable of catalysing protein folding in vitro, to associate with nascent cytosolic and secretory polypeptiDA chains, and to cooperate with the GroEL chaperone in promoting proteolysis of an unstable polypeptiDA in vivo. These findings suggest roles for trigger factor in various folding processes of secretory as well as cytosolic proteins.
