Trigger factor interacts with DnaA protein to stimulate its interaction with DnaA box

While screening proteins that interact with DnaA protein, the initiator protein for Escherichia coli chromosomal DNA replication, we found a 52‐kD sized protein which bound to DnaA protein in a salt‐dependent manner. This protein was identified as trigger factor, a ribosome‐associated peptidyl‐prolyl‐cis/trans isomerase with chaperone activity. Trigger factor was overproduced and purified to near homogeneity, and its effect on the function of DnaA protein was examined. Enhanced binding of DnaA protein to DnaA box with no apparent super shift in the gel‐shift experiments suggested that trigger factor, by virtue of its chaperone activity, exerts a change on DnaA protein thus increasing its binding affinity for DnaA box.