TRANSCRIPTION OF FTSZ OSCILLATES DURING THE CELL-CYCLE OF ESCHERICHIA-COLI

The FtsZ protein is a key element controlling cell division in Escheri chia coli. A powerful transcription titration assay was used to quanti fy the ftsZ mRNA present in synchronously dividing cells. The ftsZ mRN A levels oscillate during the cell cycle reaching a maximum at about t he time DNA replication initiates. This cell cycle dependency is speci fically due to the two proximal ftsZ promoters. A strain was construct ed in which expression of ftsZ could be modulated by an exogenous indu cer. In this strain cell size and cell division frequency were sensiti ve to the cellular FtsZ contents, demonstrating the rate-limiting role of this protein in cell division. Transcriptional activity of the fts Z promoters was found to be independent of DnaA, indicating that DNA r eplication and cell division may be independently controlled at the ti me when new rounds of DNA replication are initiated. This suggests a p arallelism between the prokaryotic cell cycle signals and the START po int of eukaryotic cell cycles.