Cell division control in Escherichia coli K-12: some properties of the ftsZ84 mutation and suppression of this mutation by the product of a newly identified gene.

The Fts proteins play an important role in the control of cell division in Escherichia coli. These proteins, which possibly form a functional complex, are encoded by genes that form an operon. In this study, we examined the properties of the temperature-sensitive mutation ftsZ84 harbored by low- or high-copy-number plasmids. Cells of strain AB1157, which had the ftsZ84 mutation, did not form colonies on salt-free L agar at 30 degrees C. When a low-copy-number plasmid containing the ftsZ84 mutation was present in these mutant cells, colony formation was restored on this medium at 30 degrees C, suggesting that FtsZ84 is probably less active than the wild-type protein and is therefore limiting in its capacity to trigger cell divisions. On the other hand, when the ftsZ84 mutation was harbored by the high-copy-number plasmid pBR325, colony formation was prevented on salt-free L agar plates whether the recipients were ftsZ84 mutant or parental cells, suggesting that, at high levels, FtsZ84 acts as a division inhibitor. The fact that colony formation was also prevented at 42 degrees C indicates that the FtsZ84 protein is not inactivated at the nonpermissive temperature. The possibility that FtsZ84 is a more efficient division inhibitor than the wild-type FtsZ is discussed. Evidence is also presented showing that a gene adjacent to mutT codes for a product that, under certain conditions, suppresses the ftsZ84 mutation.