Analysis of pBR322 replication kinetics and its dependency on growth rate

Accurate estimates of plasmid copy number in a cell are a prerequisite for predicting plasmid stability and protein production. A refined version of a structured model for the pBR322 plasmid replication mechanism is described. The model is capable of accurately predicting pBR322 plasmid copy number in Escherichia coli B/r for a wide range of growth rates. The refinements include better estimates of promoter strength, the degradation rate of RNA species, binding constant of RNAI-RNAII reaction, and dependency of promoter strength on growth rate. The predictions of the model are verified by recent experimental observations but differ from some previous reports. This model can also be used to predict the binding constant of the RNAI-RNAII reaction of ColE1 type plasmids. At 37 degrees C, the binding constant is estimated to be 77 +/- 11 x 10(-13) mL/molecule-h for pBR322.