Only the N-Terminal Domain of FtsK Functions in Cell Division

Deletion of ftsK results in the inhibition of cell division, but this inhibition can be reversed by a plasmid carrying only the first ∼17% of ftsK. The division block can be suppressed in most mutants by deletion of dacA, which codes for the d-alanine:d-alanine carboxypeptidase PBP5, or in all mutants by overexpression of ftsN. Overexpression of ftsK inhibits cell division and the formation of FtsZ rings. This division block is not due to the induction of either the SOS or the heat shock regulons.The ftsK gene of Escherichia coli encodes a large protein (1,329 amino acids) which belongs to a family of bacterium- and plasmid-encoded proteins (2), at least some of which are required for DNA transfer between cells (12, 14, 17, 23) or between a mother cell and a spore compartment (24, 25). The FtsK protein is predicted to have an N-terminal domain (of about 200 amino acids) with several (four or five) membrane-spanning α helices, a proline-glutamine-rich region (∼660 amino acids), and a cytoplasmic domain (∼469 amino acids) with a consensus nucleotide-binding pocket (2). Two independent missense mutations (ftsK44 and ftsK3531) cause different single-amino-acid substitutions in the N-terminal domain, resulting in a temperature-dependent block of cell division (2; unpublished data). The division defect in both of these mutants can be suppressed by deletion of the dacA gene, coding for a d-alanine:d-alanine carboxypeptidase (PBP5), and can be complemented by cloned fragments of the wild-type ftsK gene that contain only the first 600 to 700 bp (2; unpublished data). The temperature sensitivity of cells carrying the ftsK44 or ftsK3531 allele is suppressed by plasmids carrying ftsN (17a).The present report describes the effects of disruption, deletion, and overexpression of the ftsK gene. We conclude that only the N-terminal ∼200-amino-acid domain of FtsK is required for cell division and that deletion of the remainder of the protein is not lethal. The ftsK gene is preceded by an SOS-inducible promoter, P_dinH (19, 20), and we show here that overexpression of FtsK blocks cell division in an SfiA-independent manner. It is therefore possible that ftsK overexpression forms part of an SfiA-independent, SOS-inducible division block.