Transcription of ftsZ oscillates during the cell cycle of Escherichia coli.

The FtsZ protein is a key element controlling cell division in Escherichia coli. A powerful transcription titration assay was used to quantify the ftsZ mRNA present in synchronously dividing cells. The ftsZ mRNA levels oscillate during the cell cycle reaching a maximum at about the time DNA replication initiates. This cell cycle dependency is specifically due to the two proximal ftsZ promoters. A strain was constructed in which expression of ftsZ could be modulated by an exogenous inducer. In this strain cell size and cell division frequency were sensitive to the cellular FtsZ contents, demonstrating the rate-limiting role of this protein in cell division. Transcriptional activity of the ftsZ promoters was found to be independent of DnaA, indicating that DNA replication and cell division may be independently controlled at the time when new rounds of DNA replication are initiated. This suggests a parallelism between the prokaryotic cell cycle signals and the START point of eukaryotic cell cycles.