Regulation of cell division in Escherichia coli: properties of new ftsZ mutants.

Cells of Escherichia coli which produce high levels of the sfiA protein are UV-sensitive and filament extensively. It has been postulated that the sfiA protein is a division inhibitor which interacts with the ftsZ protein (formerly called sfiB or sulB) leading to cell division arrest. Under certain conditions, a similar division inhibition is observed with cells harboring a mutationally altered tsM allele, another division gene which was postulated to code for a division inhibitor or a controlling effector thereof (Drapeau et al. (1984). In this communication, we report on the properties of ftsZ mutants isolated under conditions which brought no selective pressure. These mutants have either an increased sensitivity to UV irradiation or filament drastically following a nutritional shift-up, or both, or even cannot grow in a rich medium. They presumably possess a ftsZ protein which responds more readily to the inhibitory action of the wild type sfiA or the mutationally altered tsM1 protein since the phenotypic expressions associated with the mutations are not observed in the presence of the sfiA11 mutation or are amplified when the ftsZ mutant cells harbor the tsM1 allele. These results further support earlier suggestions that sfiA modulates ftsZ activity and establish tsM as an additional regulatory element thereof. In addition, it is shown that E. coli strain B is a naturally occurring ftsZ mutant.