A new Escherichia coli cell division gene, ftsK

The universal stress protein A of Escherichia coli is required for resistance to DNA damaging agents and is regulated by a RecA/FtsK-dependent regulatory pathway

The link between cell division defects and the induction of the universal stress response is demonstrated to operate via the RecA regulator of the SOS response. An insertion in the cell division gene ftsK upregulates uspA in a recA-dependent manner. Unlike true SOS response genes, this upregulation only occurs in growth-arrested cells and is LexA independent. Thus, besides ppGpp-dependent starvation signals, DNA aberrations transduce RecA-dependent signals to the uspA promoter, which only affect the promoter during stasis. Further, we show that ftsK itself, like uspA, is induced in stationary phase and that this induction requires the stringent control modulon rather than activated RecA. Thus, ftsK, like uspA, is regulated by at least two global regulators: ppGpp of the stringent control network and RecA of the SOS modulon. We suggest that UspA is a new bona fide member of the RecA-dependent DNA protection and repair system, as mutants lacking functional UspA were found to be sensitive to UV irradiation and mitomycin C exposure. Moreover, the UV sensitivity of uspA mutants is enhanced in an additive manner by the ftsK1 mutation.

Color-coding reveals tandem repeats in the Escherichia coli genome

Genomic DNA contains a wide variety of repetitive sequences. In Escherichia coli, there have been several classes of repetitive sequences reported, some of which cluster as tandem repeats. We propose a novel method for analyzing symbolic sequences by two-dimensional pattern formation with color-coding. We applied this method for searching tandem repeats in the E. coli genome and found approximately 50 repeats with periods longer than 30 bases. The longest repeat has a period of 1267 bases.

Bacterial cell division

Formation of the bacterial division septum is catalyzed by a number of essential proteins that assemble into a ring structure at the future division site. Assembly of proteins into the cytokinetic ring appears to occur in a hierarchial order that is initiated by the FtsZ protein, a structural and functional analog of eukaryotic tubulins. Placement of the division site at its correct location in Escherichia coli requires a division inhibitor (MinC), that is responsible for preventing septation at unwanted sites near the cell poles, and a topological specificity protein (MinE), that forms a ring at midcell and protects the midcell site from the division inhibitor. However, the mechanism responsible for identifying the position of the midcell site or the polar sites used for spore septum formation is still unclear. Regulation of the division process and its coordination with other cell cycle events, such as chromosome replication, are poorly understood. However, a protein has been identified in Caulobacter (CtrA) that regulates both the initiation of chromosome regulation and the transcription of ftsZ, and that may play an important role in the coordination process.

The putative DNA translocase SpoIIIE is required for sporulation of the symmetrically dividing coccal species Sporosarcina ureae

The spoIIIE gene of Sporosarcina ureae encodes a 780-residue protein, showing 58% identity to the SpoIIIE protein of Bacillus subtilis, which is thought to be a DNA translocase. Expression of the S. ureae spoIIIE gene is able to restore sporulation in a B. subtilis spoIIIE mutant. Inactivation of the S. ureae spoIIIE gene blocks sporulation of S. ureae at stage III. Within the limits of detection, the sporulation division in S. ureae shows the same symmetry, or near symmetry, as the vegetative division (in contrast to the highly asymmetric location of the sporulation division for B. subtilis), and so it is inferred that SpoIIIE facilitates chromosome partitioning during sporulation, even when the division is not grossly asymmetric. It is suggested that chromosome partitioning lags behind division during sporulation but not during vegetative growth.

Norfloxacin-induced DNA cleavage occurs at the dif resolvase locus in Escherichia coli and is the result of interaction with topoisomerase IV

The dif locus is a site-specific recombination site located within the terminus region of the chromosome of Escherichia coli. Recombination at dif resolves circular dimer chromosomes to monomers, and this recombination requires the XerC, XerD and FtsK proteins, as well as cell division. In order to characterize other enzymes that interact at dif, we tested whether quinolone-induced cleavage occurs at this site. Quinolone drugs, such as norfloxacin, inhibit the type 2 topoisomerases, DNA gyrase and topoisomerase IV, and can cleave DNA at sites where these enzymes interact with the chromosome. Using strains in which either DNA gyrase or topoisomerase IV, or both, were resistant to norfloxacin, we determined that specific interactions between dif and topoisomerase IV caused cleavage at that site. This interaction required XerC and XerD, but did not require the C-terminal region of FtsK or cell division.

The cytoplasmic domain of FtsK protein is required for resolution of chromosome dimers

Chromosome dimers, formed by homologous recombination between sister chromosomes, normally require cell division to be resolved into monomers by site-specific recombination at the dif locus of Escherichia coli. We report here that it is not in fact cell division per se that is required for dimer resolution but the action of the cytoplasmic domain of FtsK, which is a bifunctional protein required both for cell division and for chromosome partition.

Role of the C terminus of FtsK in Escherichia coli chromosome segregation

FtsK is essential for Escherichia coli cell division. We report that cells lacking the C terminus of FtsK are defective in chromosome segregation as well as septation, often exhibiting asymmetrically positioned nucleoids and large anucleate regions. Combining the corresponding truncated ftsK gene with a mukB null mutation resulted in a synthetic lethal phenotype. When the truncated ftsK was combined with a minCDE deletion, chains of minicells were generated, many of which contained DNA. These results suggest that the C terminus of FtsK has an important role in chromosome partitioning.

The conjugative plasmid pSG5 from Streptomyces ghanaensis DSM 2932 differs in its transfer functions from other Streptomyces rolling-circle-type plasmids

The Streptomyces ghanaensis plasmid pSG5 is self-transmissible but does not form the growth-retardation zones (pocks) normally characteristic of the Streptomyces plasmid-transfer process. The complete nucleotide sequence of pSG5 was determined on both strands. pSG5 is 12,208 bp in length and has a GC content of 68 mol%. Characterization of the open reading frames by insertion and deletion analysis revealed that only a single gene, traB, is involved in the transfer of pSG5. The deduced amino acid sequence of TraB is similar to the SpoIIIE protein that is responsible for chromosome translocation during prespore formation of Bacillus subtilis. In contrast to the tra genes of the other Streptomyces plasmids, the pSG5 traB does not represent a kill function. Although pSG5 transfer is not associated with pock formation, pSG5 was shown to possess putative spd genes that are responsible for the pock phenotype of other Streptomyces plasmids. However, promoter-probe experiments revealed that the spd genes of pSG5 are not transcribed, thus explaining the deficiency in pock formation.

Nucleotide sequence and characterization of cdrA, a cell division-related gene of Helicobacter pylori

We identified cell division-related gene cdrA in Helicobacter pylori HPK5. The putative gene product, CdrA, is a 367-amino-acid polypeptide that exhibited a high level of homology to conserved hypothetical ATP-binding protein HP0066 of H. pylori 26695, except in the N-terminal region, and showed some similarity to the FtsK/SpoIIIE family proteins. We isolated a cdrA-disrupted mutant by allelic exchange mutagenesis. Because of the low transformation frequency, the possibility that a suppressing mutation would be found in the obtained cdrA mutant was discussed. A repressive role for CdrA on cell division was suggested by the observations that the wild-type strain formed filamentous cells in a high-salt level medium at early stationary phase, while a cdrA-disrupted mutant did not show such an abnormality. In addition, the wild-type strain adopted coccoid forms in the stationary phase, whereas the cdrA-disrupted mutant remained mostly as short rods. Furthermore, the cdrA-disrupted mutant regained the filamentation phenotype when the intact cdrA gene was introduced by allelic exchange. Taken together, these observations show that the cdrA gene plays an important role in the cell growth of H. pylori.

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 approximately 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.

Linkage map of Escherichia coli K-12, edition 10: the traditional map

This map is an update of the edition 9 map by Berlyn et al. (M. K. B. Berlyn, K. B. Low, and K. E. Rudd, p. 1715-1902, in F. C. Neidhardt et al., ed., Escherichia coli and Salmonella: cellular and molecular biology, 2nd ed., vol. 2, 1996). It uses coordinates established by the completed sequence, expressed as 100 minutes for the entire circular map, and adds new genes discovered and established since 1996 and eliminates those shown to correspond to other known genes. The latter are included as synonyms. An alphabetical list of genes showing map location, synonyms, the protein or RNA product of the gene, phenotypes of mutants, and reference citations is provided. In addition to genes known to correspond to gene sequences, other genes, often older, that are described by phenotype and older mapping techniques and that have not been correlated with sequences are included.

FtsK is an essential cell division protein that is localized to the septum and induced as part of the SOS response

The role of ftsK in the growth of Escherichia coli was examined by turning off its expression. This resulted in smooth filaments without constrictions, indicating that FtsK was required at an early step in septation. Consistent with this, FtsK was found to localize to the septum in 70% of the cells, indicating that it was recruited relatively early in this process. FtsK localization required the function of FtsZ and FtsA but not FtsI and FtsQ. Consistent with this, Z rings were present in FtsK-depleted filaments. Subcellular localization of FtsK confirmed that it was a membrane protein. Only the first 202 amino acids of FtsK were essential for its role in membrane localization, cell division and viability. The expression of ftsK increased as part of the SOS response, and increased expression of ftsK conferred increased resistance to DNA damage.

Whole sequence of spoIIIE-like, sporulation-inhibitory, and transfer gene (spi) in a conjugative plasmid, pSA1.1, of Streptomyces azureus and detection of spi-like gene in the actinomycete chromosome

The nucleotide sequence of spoIIIE-like and the sporulation-inhibitory and transfer gene (spi) in a conjugative plasmid, pSA1.1, of Streptomyces azureus were examined to detect the promoter region. Using Southern blotting and a spi fragment as probe, spi-like genes were detected in chromosomes of the host and other actinomycetes. These results suggest that there is a spi- and spoIIIE-like gene in chromosomes of some actinomycetes.

Structural homologues P(II) and P(Z) of Azospirillum brasilense provide intracellular signalling for selective regulation of various nitrogen-dependent functions

P(II) (glnB) is a signal transduction protein that in Azospirillum brasilense is specifically required for nitrogen fixation. Little is known about whether and how its homologue P(Z) (glnZ) participates in the regulation of cellular functions. In this study, we have shown the regulatory action of the two proteins by analysing the relevant single and double null-mutant strains. The transcription of glnZ is monocistronic, and it starts mainly from a sigma54-dependent promoter, activated by NtrC. glnZ expression is dependent on the ntr system, even under conditions of nitrogen excess, and is greatly enhanced in the presence of aspartate. P(Z) is uridylylated in response to nitrogen limitation, like P(II), although different amounts of the two proteins are synthesized. P(II) is required for the dephosphorylation of NtrC. Thus, in the absence of P(II), the repression of nitrate assimilation is not promoted, which, in turn, leads to a high rate of ammonium excretion. Unexpectedly, P(II) and P(Z) proteins are not essential for the reversible modification of glutamine synthetase. (Methyl)ammonium transport into the cell is negatively regulated by P(Z). The growth of a double-mutant strain (glnB::kan; glnZ::omega) is drastically disabled, although wild-type growth is restored by complementation with either glnB or glnZ. We conclude that P(II) and P(Z), despite their structural similarity, are involved in different regulatory processes, except for that required for cell growth.

FtsI and FtsW are localized to the septum in Escherichia coli

The localization of FtsI (PBP3), a penicillin-binding protein specifically required for cell division in Escherichia coli, was investigated by immunofluorescence microscopy and found to localize to the septum. The localization of FtsI was not observed in ftsZ or ftsA mutants, indicating that it was dependent on the prior localization of these proteins. Addition of furazlocillin, a specific inhibitor of FtsI, prevented localization of FtsI even though FtsZ and FtsA localization occurred. Interestingly, the localization of FtsN was also prevented by furazlocillin. FtsZ displayed limited localization in furazlocillin-treated cells, whereas it was efficiently localized in FtsI-depleted cells. FtsW, another essential cell division protein, was also localized to the septum.

Mutagenesis and more: umuDC and the Escherichia coli SOS response

The cellular response to DNA damage that has been most extensively studied is the SOS response of Escherichia coli. Analyses of the SOS response have led to new insights into the transcriptional and post-translational regulation of processes that increase cell survival after DNA damage as well as insights into DNA-damage-induced mutagenesis, i.e., SOS mutagenesis. SOS mutagenesis requires the recA and umuDC gene products and has as its mechanistic basis the alteration of DNA polymerase III such that it becomes capable of replicating DNA containing miscoding and noncoding lesions. Ongoing investigations of the mechanisms underlying SOS mutagenesis, as well as recent observations suggesting that the umuDC operon may have a role in the regulation of the E. coli cell cycle after DNA damage has occurred, are discussed.

Morphogenesis of Escherichia coli

The shape of Escherichia coli is strikingly simple compared to those of higher eukaryotes. In fact, the end result of E. coli morphogenesis is a cylindrical tube with hemispherical caps. It is argued that physical principles affect biological forms. In this view, genes code for products that contribute to the production of suitable structures for physical factors to act upon. After introduction of a physical model, the discussion is focused on the shape-maintaining (peptidoglycan) layer of E. coli. This is followed by a detailed analysis of the structural relationship of the cellular interior to the cytoplasmic membrane. A basic theme of this review is that the transcriptionally active nucleoid and the cytoplasmic translation machinery form a structural continuity with the growing cellular envelope. An attempt has been made to show how this dynamic relationship during the cell cycle affects cell polarity and how it leads to cell division.

Localization of cell division protein FtsK to the Escherichia coli septum and identification of a potential N-terminal targeting domain

Escherichia coli cell division protein FtsK is a homolog of Bacillus subtilis SpoIIIE and appears to act late in the septation process. To determine whether FtsK localizes to the septum, we fused three N-terminal segments of FtsK to green fluorescent protein (GFP) and expressed them in E. coli cells. All three segments were sufficient to target GFP to the septum, suggesting that as little as the first 15% of the protein is a septum-targeting domain. Localized fluorescence was detectable only in cells containing a visible midcell constriction, suggesting that FtsK targeting normally occurs only at a late stage of septation. The largest two FtsK-GFP fusions were able at least partially to complement the ftsK44 mutation in trans, suggesting that the N- and C-terminal domains are functionally separable. However, overproduction of FtsK-GFP resulted in a late-septation phenotype similar to that of ftsK44, with fluorescent dots localized at the blocked septa, suggesting that high levels of the N-terminal domain may still localize but also inhibit FtsK activity. Interestingly, under these conditions fluorescence was also sometimes localized as bands at potential division sites, suggesting that FtsK-GFP is capable of targeting very early. In addition, FtsK-GFP localized to potential division sites in cephalexin-induced and ftsI mutant filaments, further supporting the idea that FtsK-GFP can target early, perhaps by recognizing FtsZ directly. This hypothesis was supported by the failure of FtsK-GFP to localize in ftsZ mutant filaments. In ftsK44 mutant filaments, FtsA and FtsZ were usually localized to potential division sites between the blocked septa. When the ftsK44 mutation was incorporated into the FtsK-GFP fusions, localization to midcell ranged between very weak and undetectable, suggesting that the FtsK44 mutant protein is defective in targeting the septum.

Bacterial cell division

Bacteria usually divide by building a central septum across the middle of the cell. This review focuses on recent results indicating that the tubulin-like FtsZ protein plays a central role in cytokinesis as a major component of a contractile cytoskeleton. Assembly of this cytoskeletal element abutting the membrane is a key point for regulation. The characterization of FtsZ homologues in Mycoplasmas, Archaea, and chloroplasts implies that the constriction mechanism is conserved and that FtsZ can constrict in the absence of peptidoglycan synthesis. In most Eubacteria, the internal cytoskeleton must also regulate synthesis of septal peptidoglycan. The Escherichia coli septum-specific penicillin-binding protein 3 (PBP3) forms a complex with other enzymes involved in murein metabolism, suggesting a centrally located transmembrane complex capable of splicing multiple new strands of peptidoglycan into the cell wall. Important questions remain about the spatial and temporal control of bacterial division.

The role of GTP-binding proteins in mechanochemical movements of microorganisms and their potential to form filamentous structures

Prokaryotic cells contain proteins which form extended chains or multimers that oscillate between monomers and oligomers of varying length. Hydrolysis of nucleoside triphosphates combined with site-specific disposition of substrates and products to monomers and multimers is the driving force of dynamic instability of these molecules. Polymeric structures are connected in some manner to a variety of signaling systems that adhere to the polymeric matrix, including the GTP-binding protein(s), protein kinases and phosphatases, and other proteins or systems that communicate between the cytoplasmic membrane and the cytosol. Flexible organization allowing regulated dynamic movement is one of the key elements in all living cells. In eukaryotic cells actin and tubulin are the two main components of dynamically controlled spatial system. These proteins are noteworthy for their ability to polymerize, reversibly, into filaments or microtubules in association with hydrolysis of ATP or GTP, respectively. As such, they regulate most of the mechanics of cell movement including cell division, cell differentiation, phagocytosis and other dynamic phenomena. Recent evidence revealed that microbial cells create functional domains at specific sites of the cells and can form cytoplasmic tubules and fibers.

A mutation in the ftsK gene of Escherichia coli affects cell-cell separation, stationary-phase survival, stress adaptation, and expression of the gene encoding the stress protein UspA

An insertional mutation in ftsK, encoding an Escherichia coli product similar to the sporulation protein SpoIIIE of Bacillus subtilis, results in uspA overexpression in stationary phase and impairs cell division. The ftsK1::cat insertion mutant forms chains which are the result of inhibited cell-cell separation, while chromosome synthesis and partitioning appear to be normal as judged by flow cytometry and electron and light microscopy in combination with DNA staining. The cells of the chains are attached to each other by a small envelope structure, and unlike in a spoIIIE mutant of B. subtilis, there is no DNA trapped in the division plane. In addition, plasmids harboring a truncated ftsK allele lacking the last 195 bp of the gene cause chain formation in wild-type cells. While the mutant cells grow at essentially the same rate as the parent in complex and defined minimal media, they are sensitive to stresses. Specifically, the mutant failed to grow at elevated salt concentrations and survived stationary phase poorly. The phenotypes of the ftsK1::cat mutant are complemented by the 3' end (spoIIIE-like half) of the ftsK locus. In contrast, the 5' end of the ftsK locus reported to complement ftsK44(Ts) phenotypes does not complement the phenotypes of the ftsK1::cat mutant.

A nonswarming mutant of Proteus mirabilis lacks the Lrp global transcriptional regulator

Proteus swarming is the rapid cyclical population migration across surfaces by elongated cells that hyperexpress flagellar and virulence genes. The mini-Tn5 transposon mutant mns2 was isolated as a tight nonswarming mutant that did not elongate or upregulate flagellar and hemolysin genes. Individual cell motility was retained but was reduced. The transposon had inserted in the gene encoding the global transcriptional regulator Lrp (leucine-responsive regulatory protein), expression of which was upregulated in differentiating swarm cells. Swarming was restored to the lrp mutant by artificial overexpression of the flhDC flagellar regulatory master operon. Lrp may be a key component in generating or relaying signals that are required for flagellation and swarming, possibly acting through the flhDC operon.

Two polypeptide products of the Escherichia coli cell division gene ftsW and a possible role for FtsW in FtsZ function

Two new mutations in the cell division gene ftsW have been isolated and characterized. The ftsW263(Ts) mutation results in a block to division at the initiation stage, similar to that previously observed with the ftsW201(Ts) mutation. The ftsW1640(Ts) mutation, however, causes a block to division at a later stage. The ftsW201 and ftsW263 mutants were shown to be phenotypically sensitive to the genetic background and growth conditions and are possibly relA dependent. Immunofluorescence microscopy showed that the FtsZ protein can localize to presumptive division sites in strains carrying ftsW(Ts) mutations at the nonpermissive temperature, suggesting that FtsW is unlikely to be specifically required for the localization of FtsZ to the division site. Examination of the localization of FtsZ in an ftsW rodA double mutant (lemon-shaped cells) revealed several classes of cells ranging from a common class where an FtsZ ring structure is absent to a class where FtsZ forms a complete ring at the midpoint of a lemon-shaped cell, suggesting a role for FtsW in the establishment of a stable FtsZ-based septal structure. We further demonstrate that two FtsW peptides, FtsWL (large) and FtsWS (small), can be identified and that the expression of ftsWS is sufficient for complementation of ftsW(Ts) mutations.

Direct binding of FtsZ to ZipA, an essential component of the septal ring structure that mediates cell division in E. coli

FtsZ is a soluble, tubulin-like GTPase that forms a membrane-associated ring at the division site of bacterial cells. While this ring is thought to drive cell constriction, it is not well understood how it is assembled or how it affects cell wall invagination. Here we report that FtsZ binds directly to a novel integral inner membrane protein in E. coli that we call ZipA. We present genetic and morphological evidence indicating that this interaction is required for cell division, and show that a fluorescent ZipA-Gfp fusion protein is located in a ring structure at the division site, both before and during cell wall invagination. ZipA is an essential component of the division machinery, and, by binding to both FtsZ and the cytoplasmic membrane, is likely to be directly involved in the assembly and/or function of the FtsZ ring.

Inactivation of FtsI inhibits constriction of the FtsZ cytokinetic ring and delays the assembly of FtsZ rings at potential division sites

A universally conserved event in cell division is the formation of a cytokinetic ring at the future site of division. In the bacterium Escherichia coli, this ring is formed by the essential cell division protein FtsZ. We have used immunofluorescence microscopy to show that FtsZ assembles early in the division cycle, suggesting that constriction of the FtsZ ring is regulated and supporting the view that FtsZ serves as a bacterial cytoskeleton. Assembly of FtsZ rings was heterogeneously affected in an ftsI temperature-sensitive mutant grown at the nonpermissive temperature, some filaments displaying a striking defect in FtsZ assembly and others displaying little or no defect. By using low concentrations of the beta-lactams cephalexin and piperacillin to specifically inhibit FtsI (PBP3), an enzyme that synthesizes peptidoglycan at the division septum, we show that FtsZ ring constriction requires the transpeptidase activity of FtsI. Unconstricted FtsZ rings are stably trapped at the midpoint of the cell for several generations after inactivation of FtsI, whereas partially constricted FtsZ rings are less effectively trapped. In addition, FtsZ rings are able to assemble in newborn cells in the presence of cephalexin, suggesting that newborn cells contain a site at which FtsZ can assemble (the nascent division site) and that the transpeptidase activity of FtsI is not required for assembly of FtsZ at these sites. However, aside from this first round of FtsZ ring assembly, very few additional FtsZ rings assemble in the presence of cephalexin, even after several generations of growth. One interpretation of these results is that the transpeptidase activity of FtsI is required, directly or indirectly, for the assembly of nascent division sites and thereby for future assembly of FtsZ rings.

Bacterial cell division and the Z ring

Bacterial cell division occurs through the formation of an FtsZ ring (Z ring) at the site of division. The ring is composed of the tubulin-like FtsZ protein that has GTPase activity and the ability to polymerize in vitro. The Z ring is thought to function in vivo as a cytoskeletal element that is analogous to the contractile ring in many eukaryotic cells. Evidence suggests that the Z ring is utilized by all prokaryotic organisms for division and may also be used by some eukaryotic organelles. This review summarizes our present knowledge about the formation, function, and evolution of the Z ring in prokaryotic cell division.

dacD, an Escherichia coli gene encoding a novel penicillin-binding protein (PBP6b) with DD-carboxypeptidase activity

In the course of a study of genes located at min 44 of the Escherichia coli genome, we identified an open reading frame with the capacity to encode a 43-kDa polypeptide whose predicted amino acid sequence is strikingly similar to those of the well-known DD-carboxipeptidases penicillin-binding proteins PBP5 and PBP6. The gene product was shown to bind [3H]benzylpenicillin and to have DD-carboxypeptidase activity on pentapeptide muropeptides in vivo. Therefore, we called the protein PBP6b and the gene dacD. As with other E. coli DD-carboxypeptidases, PBP6b is not essential for cell growth. A quadruple dacA dacB dacC dacD mutant was constructed and shown to grow as well as its isogenic wild-type strain, indicating that the loss of any known PBP-associated DD-carboxypeptidase activity is not deleterious for E. coli. We also identified the homologous gene of dacD in Salmonella typhimurium as one of the components of the previously described phsBCDEF gene cluster.

Structure, function and controls in microbial division

Several crucial genes required for bacterial division lie close together in a region called the dcw cluster. Within the cluster, gene expression is subject to complex transcriptional regulation, which serves to adjust the cell cycle in response to growth rate. The pivotally important FtsZ protein, which is needed to initiate division, is now known to interact with many other components of the division machinery in Escherichia coli. Some biochemical properties of FtsZ, and of another division protein called FtsA, suggest that they are similar to the eukaryotic proteins tubulin and actin respectively. Cell division needs to be closely co-ordinated with chromosome partitioning. The mechanism of partitioning is poorly understood, though several genes involved in this process, including several muk genes, have been identified. The min genes may participate in both septum positioning and chromosome partitioning. Coupled transcription and translation of membrane-associated proteins might also be important for partitioning. In the event of a failure in the normal partitioning process, Bacillus subtilis, at least, has a mechanism for removing a bisected nucleoid from the division septum.