SpoIIIE and a novel type of DNA translocase, SftA, couple chromosome segregation with cell division in Bacillus subtilis

Abstract

SummaryCell division must only occur once daughter chromosomes have been fully separated. However, the initiating event of bacterial cell division, assembly of the FtsZ ring, occurs while chromosome segregation is still ongoing. We show that a two-step DNA translocase system exists in Bacillus subtilis that couples chromosome segregation and cell division. The membrane-bound DNA translocase SpoIIIE assembled very late at the division septum, and only upon entrapment of DNA, while its orthologue, SftA (YtpST), assembled at each septum in B. subtilis soon after FtsZ. Lack of SftA resulted in a moderate segregation defect at a late stage in the cell cycle. Like the loss of SpoIIIE, the absence of SftA was deleterious for the cells during conditions of defective chromosome segregation, or after induction of DNA damage. Lack of both proteins exacerbated all phenotypes. SftA forms soluble hexamers in solution, binds to DNA and has DNA-dependent ATPase activity, which is essential for its function in vivo. Our data suggest that SftA aids in moving DNA away from the closing septum, while SpoIIIE translocates septum-entrapped DNA only when septum closure precedes complete segregation of chromosomes.

Contribution of SMC (Structural Maintenance of Chromosomes) and SpoIIIE to Chromosome Segregation in Staphylococci

“…SftA translocates chromosomes before septation, while SpoIIIE comes into play postseptationally when chromosomes are trapped by the septal membrane. Like B. subtilis spoIIIE mutants, the sftA mutants had a synergistic lethal defect with an smc deletion (18). The B. subtilis sftA spoIIIE double mutant undergoes normal growth, while the defect in chromosome segregation is exacerbated significantly compared to that in both single mutants.…”

“…192, 2010 NOTES 4071 other factors that play more significant roles in chromosome partitioning in cocci than in rods need to be identified. Recently it has been found in B. subtilis that a second FtsK/SpoIIIE-like protein, SftA (septum-associated FtsKlike translocase of DNA), coordinates chromosome translocation to ensure maximum chromosome segregation, however, at a different stage of cell division from SpoIIIE (2,18). SftA contains the C-terminal DNA binding and ATPase domain, but instead of the N-terminal transmembrane domain in SpoIIIE, it has a soluble domain.…”

The Putative Hydrolase YycJ (WalJ) Affects the Coordination of Cell Division with DNA Replication inBacillus subtilisand May Play a Conserved Role in Cell Wall Metabolism

“…As a proof of principle, we found that cells lacking the nucleoid occlusion protein Noc, which divide over unsegregated chromosomes more frequently than wild-type cells when DNA replication is blocked (77), required functional SpoIIIE for growth on agar plates only when DNA replication was repeatedly inhibited (8). One gene identified in the screen, sftA, encodes a paralog of SpoIIIE that appears to play a specialized role in promoting the efficient completion of chromosome segregation when cells divide (8,36,74).…”

“…For example, a number of mechanisms function to ensure proper localization of the cytokinetic Z-ring and control the assembly and activity of the division machinery at the septum (1,3,24,29,46). During the late stages of cell division in Bacillus subtilis, a DNA translocase (SftA) helps ensure that chromosomes are fully segregated into daughter cells before septation is completed (8,36). Failure to properly coordinate the stages of the cell cycle can lead to aberrant division events where the septum forms over the chromosome and results in at least one daughter cell lacking a complete copy of the genome.…”

“…As a proof of principle, we found that cells lacking the nucleoid occlusion protein Noc, which divide over unsegregated chromosomes more frequently than wild-type cells when DNA replication is blocked (77), required functional SpoIIIE for growth on agar plates only when DNA replication was repeatedly inhibited (8). One gene identified in the screen, sftA, encodes a paralog of SpoIIIE that appears to play a specialized role in promoting the efficient completion of chromosome segregation when cells divide (8,36,74).As a complement to our genetic screen, we took a bioinformatic approach to identify Noc-like proteins based on the hypothesis that there could be physical or genetic interactions between Noc and other proteins involved in preventing aberrant cell divisions. We searched the Stanford Network Browser (http://networks.stanford.edu), a database for inferring functional interactions between bacterial genes based on the coevolution of conserved domains, cooccurrence within sequenced genomes, gene proximity, and a limited number of data sets from whole-genome expression analysis (26,65).…”