The Fis protein has a stimulating role in initiation of replication in Escherichia coli in vivo.

The Fis protein is a nucleoid associated protein that has previously been reported to act negatively in initiation of replication in Escherichia coli. In this work we have examined the influence of this protein on the initiation of replication under different growth conditions using flow cytometry. The Fis protein was found to be increasingly important with increasing growth rate. During multi-fork replication severe under-initiation occurred in cells lacking the Fis protein; the cells initiated at an elevated mass, had fewer origins per cell and the origins were not initiated in synchrony. These results suggest a positive role for the Fis protein in the initiation of replication.