A protein binding to an upstream sequence of ftsZ involved in coordination of DNA replication and cell division in Microcystis aeruginosa

The cyanobacterium Microcystis aeruginosa frequently forms blooms in eutrophic freshwater. Previously, we demonstrated that DNA replication and cell division are coordinated in M. aeruginosa NIES 298, and some part of this coordination is mediated by transcriptional regulation of the cell division gene ftsZ . In this study, to search for regulators involved in regulation of ftsZ transcription, we performed gel electrophoresis mobility shift assays (EMSA) using oligonucleotide probes corresponding to upstream sequences of ftsZ . Sequential EMSA analysis detected a protein binding to a 35-bp sequence ( Fz35A ) just upstream from the ftsZ start codon. Addition of excess unlabeled Fz35A caused disappearance of the retarded band, clearly indicating that this protein binds specifically to this sequence. While sequence comparison in cyanobacteria revealed conserved bases T-CC···T-CA among phylogenetically related species of Microcystis , mutation of these bases did not completely inhibit protein binding, suggesting that T-CC···T-CA contain at least one or more bases which are important to protein–DNA interaction. When EMSA was performed using crude protein extract from cells with DNA replication blocked, band shift was not observed. These data suggest that the protein factor may be involved in coordination of DNA replication and cell division via transcription control of ftsZ in M. aeruginosa .