Identification of new genes in a cell envelope-cell division gene cluster of Escherichia coli: cell envelope gene murG

Screening of potential phytomolecules against MurG as drug target in nosocomial pathogen Pseudomonas aeruginosa: perceptions from computational campaign

The nosocomial infection outbreak caused by Pseudomonas aeruginosa remains a public health concern. Multi-drug resistant (MDR) strains of P. aeruginosa are rapidly spreading leading to a huge mortality rate because of the unavailability of promising antimicrobials. MurG glycotransferase [UDP-N-acetylglucosamine-N-acetylmuramyl (pentapeptide) pyrophosphoryl-undecaprenol N-acetylglucosamine transferase] is located at the plasma membrane and plays a key role in murein (peptidoglycan) biosynthesis in bacteria. Since MurG is required for bacterial cell wall synthesis and is non-homologous to Homo sapiens; it can be a potential target for the antagonist to treat P. aeruginosa infection. The discovery of high-resolution crystal structure of P. aeruginosa MurG offers an opportunity for the computational identification of its prospective inhibitors. Therefore, in the present study, the crystal structure of MurG (PDB ID: 3S2U) from P. aeruginosa was selected, and computational docking analyses were performed to search for functional inhibitors of MurG. IMPPAT (Indian medicinal plants, phytochemicals and therapeutic) phytomolecule database was screened by computational methods with MurG catalytic site. Docking results identified Theobromine (-8.881 kcal/mol), demethoxycurcumin (-8.850 kcal/mol), 2-alpha-hydroxycostic acid (-8.791 kcal/mol), aurantiamide (-8.779 kcal/mol) and petasiphenol (-8.685 kcal/mol) as a potential inhibitor of the MurG activity. Further, theobromine and demethoxycurcumin were subjected to MDS (molecular dynamics simulation) and free energy (MM/GBSA) analysis to comprehend the physiological state and structural stability of MurG-phytomolecules complexes. The outcomes suggested that these two phytomolecules could act as most favorable natural hit compounds for impeding the enzymatic action of MurG in P. aeruginosa, and thus it needs further validation by both in vitro and in vivo analysis. HIGHLIGHTSThe top phytomolecules such as theobromine, demethoxycurcumin, 2-alpha-hydroxycostic acid, aurantiamide and petasiphenol displayed promising binding with MurG catalytic domain.MurG complexed with theobromine and demethoxycurcumin showed the best interaction and stable by MD simulation at 100 ns.The outcome of MurG binding phytomolecules has expanded the possibility of hit phytomolecules validation.Communicated by Ramaswamy H. Sarma.

I am better than I look: genome based safety assessment of the probiotic Lactiplantibacillus plantarum IS-10506

BACKGROUND

Safety of probiotic strains that are used in human and animal trials is a prerequisite. Genome based safety assessment of probiotics has gained popularity due its cost efficiency and speed, and even became a part of national regulation on foods containing probiotics in Indonesia. However, reliability of the safety assessment based only on a full genome sequence is not clear. Here, for the first time, we sequenced, assembled, and analysed the genome of the probiotic strain Lactiplantibacillus plantarum IS-10506, that was isolated from dadih, a traditional fermented buffalo milk. The strain has already been used as a probiotic for more than a decade, and in several clinical trials proven to be completely safe.

METHODS

The genome of the probiotic strain L. plantarum IS-10506 was sequenced using Nanopore sequencing technology, assembled, annotated and screened for potential harmful (PH) and beneficial genomic features. The presence of the PH features was assessed from general annotation, as well as with the use of specialised tools. In addition, PH regions in the genome were compared to all other probiotic and non-probiotic L. plantarum strains available in the NCBI RefSeq database.

RESULTS

For the first time, a high-quality complete genome of L. plantarum IS-10506 was obtained, and an extensive search for PH and a beneficial signature was performed. We discovered a number of PH features within the genome of L. plantarum IS-10506 based on the general annotation, including various antibiotic resistant genes (AMR); however, with a few exceptions, bioinformatics tools specifically developed for AMR detection did not confirm their presence. We further demonstrated the presence of the detected PH genes across multiple L. plantarum strains, including probiotics, and overall high genetic similarities between strains.

CONCLUSION

The genome of L. plantarum IS-10506 is predicted to have several PH features. However, the strain has been utilized as a probiotic for over a decade in several clinical trials without any adverse effects, even in immunocompromised children with HIV infection and undernourished children. This implies the presence of PH feature signatures within the probiotic genome does not necessarily indicate their manifestation during administration. Importantly, specialized tools for the search of PH features were found more robust and should be preferred over manual searches in a general annotation.

The Membrane Steps of Bacterial Cell Wall Synthesis as Antibiotic Targets

Peptidoglycan is the major component of the cell envelope of virtually all bacteria. It has structural roles and acts as a selective sieve for molecules from the outer environment. Peptidoglycan synthesis is therefore one of the most important biogenesis pathways in bacteria and has been studied extensively over the last twenty years. The pathway starts in the cytoplasm, continues in the cytoplasmic membrane and finishes in the periplasmic space, where the precursor is polymerized into the peptidoglycan layer. A number of proteins involved in this pathway, such as the Mur enzymes and the penicillin binding proteins (PBPs), have been studied and regarded as good targets for antibiotics. The present review focuses on the membrane steps of peptidoglycan synthesis that involve two enzymes, MraY and MurG, the inhibitors of these enzymes and the inhibition mechanisms. We also discuss the challenges of targeting these two cytoplasmic membrane (associated) proteins in bacterial cells and the perspectives on how to overcome the issues.

Subpolar addition of new cell wall is directed by DivIVA in mycobacteria

Mycobacteria are surrounded by a complex multilayered envelope and elongate at the poles. The principles that organize the coordinated addition of chemically diverse cell wall layers during polar extension remain unclear. We show that enzymes mediating the terminal cytosolic steps of peptidoglycan, arabinogalactan, and mycolic acid synthesis colocalize at sites of cell growth or division. The tropomyosin-like protein, DivIVA, is targeted to the negative curvature of the pole, is enriched at the growing end, and determines cell shape from this site. In contrast, cell wall synthetic complexes are concentrated at a distinct subpolar location. When viewed at subdiffraction resolution, new peptidoglycan is deposited at this subpolar site, and inert cell wall covers the DivIVA-marked tip. The differentiation between polar tip and cell wall synthetic complexes is also apparent at the biochemical level. Enzymes that generate mycolate precursors interact with DivIVA, but the final condensation of mycolic acids occurs in a distinct protein complex at the site of nascent cell wall addition. We propose an ultrastructural model of mycobacterial polar growth where new cell wall is added in an annular zone below the cell tip. This model may be broadly applicable to other bacterial and fungal organisms that grow via polar extension.

Peptidoglycan hydrolases of Escherichia coli

The review summarizes the abundant information on the 35 identified peptidoglycan (PG) hydrolases of Escherichia coli classified into 12 distinct families, including mainly glycosidases, peptidases, and amidases. An attempt is also made to critically assess their functions in PG maturation, turnover, elongation, septation, and recycling as well as in cell autolysis. There is at least one hydrolytic activity for each bond linking PG components, and most hydrolase genes were identified. Few hydrolases appear to be individually essential. The crystal structures and reaction mechanisms of certain hydrolases having defined functions were investigated. However, our knowledge of the biochemical properties of most hydrolases still remains fragmentary, and that of their cellular functions remains elusive. Owing to redundancy, PG hydrolases far outnumber the enzymes of PG biosynthesis. The presence of the two sets of enzymes acting on the PG bonds raises the question of their functional correlations. It is difficult to understand why E. coli keeps such a large set of PG hydrolases. The subtle differences in substrate specificities between the isoenzymes of each family certainly reflect a variety of as-yet-unidentified physiological functions. Their study will be a far more difficult challenge than that of the steps of the PG biosynthesis pathway.

Peptidoglycan biosynthesis machinery: a rich source of drug targets

The range of antibiotic therapy for the control of bacterial infections is becoming increasingly limited because of the rapid rise in multidrug resistance in clinical bacterial isolates. A few diseases, such as tuberculosis, which were once thought to be under control, have re-emerged as serious health threats. These problems have resulted in intensified research to look for new inhibitors for bacterial pathogens. Of late, the peptidoglycan (PG) layer, the most important component of the bacterial cell wall has been the subject of drug targeting because, first, it is essential for the survivability of eubacteria and secondly, it is absent in humans. The last decade has seen tremendous inputs in deciphering the 3-D structures of the PG biosynthetic enzymes. Many inhibitors against these enzymes have been developed using virtual and high throughput screening techniques. This review discusses the mechanistic and structural properties of the PG biosynthetic enzymes and inhibitors developed in the last decade.

The biosynthesis of peptidoglycan lipid-linked intermediates

The biosynthesis of bacterial cell wall peptidoglycan is a complex process involving many different steps taking place in the cytoplasm (synthesis of the nucleotide precursors) and on the inner and outer sides of the cytoplasmic membrane (assembly and polymerization of the disaccharide-peptide monomer unit, respectively). This review summarizes the current knowledge on the membrane steps leading to the formation of the lipid II intermediate, i.e. the substrate of the polymerization reactions. It makes the point on past and recent data that have significantly contributed to the understanding of the biosynthesis of undecaprenyl phosphate, the carrier lipid required for the anchoring of the peptidoglycan hydrophilic units in the membrane, and to the characterization of the MraY and MurG enzymes which catalyze the successive transfers of the N-acetylmuramoyl-peptide and N-acetylglucosamine moieties onto the carrier lipid, respectively. Enzyme inhibitors and antibacterial compounds interfering with these essential metabolic steps and interesting targets are presented.

Role of the amino acid invariants in the active site of MurG as evaluated by site-directed mutagenesis

To evaluate their role in the active site of the MurG enzyme from Escherichia coli, 13 residues conserved in the sequences of 73 MurG orthologues were submitted to site-directed mutagenesis. All these residues lay within, or close to, the active site of MurG as defined by its tridimensional structure [Ha et al., Prot. Sci. 9 (2000) 1045-1052, and Hu et al., Proc. Natl. Acad. Sci. USA 100 (2003) 845-849]. Thirteen mutants proteins, in which residues T15, H18, Y105, H124, E125, N127, N134, S191, N198, R260, E268, Q288 or N291 have been replaced by alanine, were obtained as the C-terminal His-tagged forms. The effects of the mutations on the activity were checked: (i) by functional complementation of an E. coli murG mutant strain by the mutated genes; and (ii) by the determination of the steady-state kinetic parameters of the purified proteins. Most mutations resulted in an important loss of activity and, in the case of N134A, in the production of a highly unstable protein. The results correlated with the assigned or putative functions of the residues based on the tridimensional structure.

The essential peptidoglycan glycosyltransferase MurG forms a complex with proteins involved in lateral envelope growth as well as with proteins involved in cell division in Escherichia coli

In Escherichia coli many enzymes including MurG are directly involved in the synthesis and assembly of peptidoglycan. MurG is an essential glycosyltransferase catalysing the last intracellular step of peptidoglycan synthesis. To elucidate its role during elongation and division events, localization of MurG using immunofluorescence microscopy was performed. MurG exhibited a random distribution in the cell envelope with a relatively higher intensity at the division site. This mid-cell localization was dependent on the presence of a mature divisome. Its localization in the lateral cell wall appeared to require the presence of MreCD. This could be indicative of a potential interaction between MurG and other proteins. Investigating this by immunoprecipitation revealed the association of MurG with MreB and MraY in the same protein complex. In view of this, the loss of rod shape of ΔmreBCD strain could be ascribed to the loss of MurG membrane localization. Consequently, this could prevent the localized supply of the lipid II precursor to the peptidoglycan synthesizing machinery involved in cell elongation. It is postulated that the involvement of MurG in the peptidoglycan synthesis concurs with two complexes, one implicated in cell elongation and the other in division. A model representing the first complex is proposed.

Identification of active-site inhibitors of MurG using a generalizable, high-throughput glycosyltransferase screen

MurG is a glycosyltransferase involved in the biosynthesis of bacterial peptidoglycan. It is a potentially important antibiotic target, but no inhibitors of the enzyme have been reported. In general, inhibitors of glycosyltransferases have been difficult to design. Furthermore, no glycosyltransferase inhibitors have been identified through high-throughput screening, perhaps because appropriate screens for glycosyltransferase inhibition have not been developed. In this manuscript, we describe the development of a high-throughput screen for MurG that was used to screen a 50 000 compound library for inhibitors. The screen, which can be generalized to other glycosyltransferases, led to the identification of a family of active-site directed MurG inhibitors. The family of inhibitors contains a five-membered heterocyclic core that appears to function as a diphosphate mimic with respect to the presentation of substituents. We discuss the implications of this result and the utility of the screen for identifying inhibitors of other glycosyltransferases.

Novel scintillation proximity assay for measuring membrane-associated steps of peptidoglycan biosynthesis in Escherichia coli

We have developed a novel, high-throughput scintillation proximity assay to measure the membrane-associated steps (stages 2 and 3) of peptidoglycan synthesis in Escherichia coli. At least five enzymes are involved in these two stages, all of which are thought to be essential for the survival of the cell. The individual enzymes are difficult to assay since the substrates are lipidic and difficult to isolate in large quantities and analysis is done by paper chromatography. We have assayed all five enzymes in a single mixture by monitoring synthesis of cross-linked peptidoglycan, which is the final product of the pathway. E. coli membranes are incubated with the two sugar precursors, UDP-N-acetyl muramylpentapeptide and UDP-[(3)H]-N-acetylglucosamine. The radiolabel is incorporated into peptidoglycan, which is captured using wheat germ agglutinin-coated scintillation proximity assay beads. The assay monitors the activity of the translocase (MraY), the transferase (MurG), the lipid pyrophosphorylase, and the transglycosylase and transpeptidase activities of the penicillin-binding proteins. Vancomyin, tunicamycin, nisin, moenomycin, bacitracin, and penicillin inhibit the assay, and these inhibitors have been used to validate the assay. The search for new antimicrobial agents that act via the late stages of peptidoglycan biosynthesis can now be performed in high throughput in a microtiter plate.

Assay for identification of inhibitors for bacterial MraY translocase or MurG transferase

Bacterial peptidoglycan synthesis is a well-characterized system for targeting new antimicrobial drugs. Formation of the peptidoglycan precursors Lipid I and Lipid II is catalyzed by the gene products of mraY and murG, which are involved in the first and second steps of the lipid cycle reactions, respectively. Here we describe the development of an assay specific for identifying inhibitors of MraY or MurG, based on the detection of radiolabeled [(14)C]GlcNAc incorporated into Lipid II. Assay specificity is achieved with the biotin tagging of the Lipid I precursor UDP-MurNAc-pentapeptide. This allows for the separation and identification of lipid products produced by the enzymatic activity of the MraY and MurG proteins, and thus identification of specific inhibitors.

UDP-N-acetylglucosamine:N-acetylmuramoyl-(pentapeptide) pyrophosphoryl undecaprenol N-acetylglucosamine transferase from Escherichia coli: overproduction, solubilization, and purification

Plasmids for the high-level overproduction of wild-type, and C- and N-terminal His-tagged MurG N-acetylglucosaminyl transferase from Escherichia coli were constructed. In complementation tests the three forms were active in vivo. After IPTG induction, growth, spheroplast formation and lysis, overproduced MurG proteins were mainly present (90%) in the particulate fraction. Readily solubilized by CHAPS, they were purified without any detergent to over 80% purity for both His-tagged forms but only up to 20% for the wild-type form. The enzymatic activity of each purified MurG protein was determined and found to be inhibited to the same extent by ramoplanin.

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.

Identification of FtsW and characterization of a new ftsW division mutant of Escherichia coli

The product of the ftsW gene has been identified as a polypeptide that, like the related RodA protein, shows anomalous mobility on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. FtsW is produced at low levels that can be increased by altering the translation initiation region of the mRNA. Overproduction of FtsW strongly inhibits cell growth. A new mutant allele, ftsW201, causes a temperature-dependent block in the initiation stage of cell division which is similar to the division block in ftsZ mutants. The block in initiation of division in the ftsW201 allele is shown to be independent of FtsZ or the FtsZ inhibitor, SulA. In addition, the ftsW201 mutant is hypersensitive to overproduction of the division initiation protein FtsZ at the permissive temperature. Our results suggest a role for FtsW in an early stage of division which may involve an interaction with FtsZ.

Identification of the Escherichia coli murI gene, which is required for the biosynthesis of D-glutamic acid, a specific component of bacterial peptidoglycan

The murI gene of Escherichia coli, whose inactivation results in the inability to form colonies in the absence of D-glutamic acid, was identified in the 90-min region of the chromosome. The complementation of an auxotrophic E. coli B/r strain by various DNA sources allowed us to clone a 2.5-kbp EcoRI chromosomal fragment carrying the murI gene into multicopy plasmids. The murI gene corresponds to a previously sequenced open reading frame, ORF1 (J. Brosius, T. J. Dull, D. D. Sleeter, and H. F. Noller. J. Bacteriol. 148:107-127, 1987), located between the btuB gene, encoding the vitamin B12 outer membrane receptor protein, and the rrnB operon, which contains the genes for 16S, 23S, and 5S rRNAs. The murI gene product is predicted to be a protein of 289 amino acids with a molecular weight of 31,500. Attempts to identify its enzymatic activity were unsuccessful. Cells altered in the murI gene accumulate UDP-N-acetylmuramyl-L-alanine to a high level when depleted of D-glutamic acid. Pools of precursors located downstream in the pathway are consequently depleted, and cell lysis finally occurs when the peptidoglycan content is 25% lower than that of normally growing cells.

The murG gene of Escherichia coli codes for the UDP-N-acetylglucosamine: N-acetylmuramyl-(pentapeptide) pyrophosphoryl-undecaprenol N-acetylglucosamine transferase involved in the membrane steps of peptidoglycan synthesis

Physiological properties of the murG gene product of Escherichia coli were investigated. The inactivation of the murG gene rapidly inhibits peptidoglycan synthesis in exponentially growing cells. As a result, various alterations of cell shape are observed, and cell lysis finally occurs when the peptidoglycan content is 40% lower than that of normally growing cells. Analysis of the pools of peptidoglycan precursors reveals the concomitant accumulation of UDP-N-acetylglucosamine (UDP-GlcNAc) and UDP-N-acetylmuramyl-pentapeptide (UDP-MurNAc-pentapeptide) and, to a lesser extent, that of undecaprenyl-pyrophosphoryl-MurNAc-pentapeptide (lipid intermediate I), indicating that inhibition of peptidoglycan synthesis occurs after formation of the cytoplasmic precursors. The relative depletion of the second lipid intermediate, undecaprenyl-pyrophosphoryl-MurNAc-(pentapeptide)GlcNAc, shows that inactivation of the murG gene product does not prevent the formation of lipid intermediate I but inhibits the next reaction in which GlcNAc is transferred to lipid intermediate I. In vitro assays for phospho-MurNAc-pentapeptide translocase and N-acetylglucosaminyl transferase activities finally confirm the identification of the murG gene product as the transferase that catalyzes the conversion of lipid intermediate I to lipid intermediate II in the peptidoglycan synthesis pathway. Plasmids allowing for a high overproduction of the transferase and the determination of its N-terminal amino acid sequence were constructed. In cell fractionation experiments, the transferase is essentially associated with membranes when it is recovered.

Structural similarity among Escherichia coli FtsW and RodA proteins and Bacillus subtilis SpoVE protein, which function in cell division, cell elongation, and spore formation, respectively

The Escherichia coli cell division gene ftsW (2 min) was cloned and sequenced. It encodes a hydrophobic protein(s) with 414 and/or 384 amino acid residues. The deduced amino acid sequence and the hydropathy profile of the protein showed high homology with those of the E. coli RodA protein functioning in determination of the cell shape and the Bacillus subtilis SpoVE protein functioning in spore formation. Probably similar functional membrane proteins are involved in these three cell cycle process.

Organization of the murE-murG region of Escherichia coli: identification of the murD gene encoding the D-glutamic-acid-adding enzyme

The 2-min region of the Escherichia coli genome contains a large cluster of genes from pbpB to envA that code for proteins involved in peptidoglycan biosynthesis and cell division. From pLC26-6 of the collection of Clarke and Carbon (L. Clarke and J. Carbon, Cell 9:91-99, 1976) plasmids carrying different fragments from the 8-kilobase-pair region downstream of pbpB were constructed and analyzed for their ability to direct protein synthesis in maxicells, to complement various thermosensitive mutations, and to overproduce enzymatic activities. We report the localization of the previously unidentified murD gene coding for the D-glutamic acid-adding enzyme within this region. Our data show that the genes are in the order pbpB-murE-murF-X-murD-Y-murG, where X and Y represent chromosomal fragments from 1 to 1.5 kilobase pairs, possibly coding for unknown proteins. Furthermore, the murE and murF genes, encoding the meso-diaminopimelic acid and D-alanyl-D-alanine-adding enzymes, respectively, may be translationally coupled when transcription is initiated upstream of murE, within the preceding structural gene pbpB coding for penicillin-binding protein 3.

New mutations fts-36, lts-33, and ftsW clustered in the mra region of the Escherichia coli chromosome induce thermosensitive cell growth and division

Three new mutants of Escherichia coli showing thermosensitive cell growth and division were isolated, and the mutations were mapped to the mra region at 2 min on the E. coli chromosome map distal to leuA. Two mutations were mapped closely upstream of ftsI (also called pbpB), in a region of 600 bases; the fts-36 mutant showed thermosensitive growth and formed filamentous cells at 42 degrees C, whereas the lts-33 mutant lysed at 42 degrees C without forming filamentous cells. The mutation in the third new thermosensitive, filament-forming mutant, named ftsW, was mapped between murF and murG. By isolation of these three mutants, about 90% of the 17-kilobase region from fts-36-lts-33 to envA could be filled with genes for cell division and growth, and the genes could be aligned.

Determination of gene products and coding regions from the murE-murF region of Escherichia coli

We report the cloning of murE and murF genes and the identification of their gene products. The murE and murF genes encode diaminopimelic acid- and D-alanyl-D-alanine-adding enzymes, respectively, and both genes are involved in cell wall peptidoglycan biosynthesis in Escherichia coli.

murH, a new genetic locus in Escherichia coli involved in cell wall peptidoglycan biosynthesis

A temperature-sensitive mutant of Escherichia coli defective in peptidoglycan synthesis was characterized. The incorporation of radiolabeled meso-diaminopimelate into peptidoglycan by the mutant was inhibited at the restrictive growth temperature, resulting in autolysis. The defective step appeared to be part of the terminal stage in peptidoglycan synthesis involving the incorporation of disaccharide peptide units into the wall peptidoglycan. The mutation was assigned to a new locus, designated murH, at 99.2 min on the E. coli linkage map.

Genetic analysis of essential genes in the ftsE region of the Escherichia coli genetic map and identification of a new cell division gene, ftsS

Several conditional lethal mutants of Escherichia coli have been analysed genetically using generalized transduction and lambda transducing vectors. Three temperature-sensitive ftsE mutants were found as was a cold-sensitive ftsE mutant. A new gene was found which mapped close to ftsE, namely ftsS. Both cell division genes map close to the gene which controls the heat-shock regulon (htpR).

Transcriptional organization within an Escherichia coli cell division gene cluster: direction of transcription of the cell separation gene envA

A cluster of at least 14 genes, each concerned with some aspect of cell envelope growth, morphogenesis, or function, is located at 2 min on the genetic map of Escherichia coli. We located the envA cell division gene and its promoter within the cluster and determined the direction of transcription of the gene by constructing fusions between its promoter and the galK coding sequence. In addition, we identified the promoter of a possible new gene lying between envA and the secA gene. We also present evidence from gene fusion studies which shows the direction of transcription of the ftsZ(sulB) division gene. The direction of transcription is the same for all three promoters and is the same as that of all other cluster genes for which this is known. We discuss the significance of this observation, together with the fact that every gene examined in sufficient detail within the cluster appears to have its own promoter and to be able to be expressed from isolated cloned fragments. Using a novel variable-copy plasmid vector, we demonstrate that the DNA fragment containing the envA gene is not stably maintained in multiple copies. The construction of two independent, nonoverlapping deletions allows us to conclude that the envA product itself is responsible for this effect.

The ftsA gene product participates in formation of the Escherichia coli septum structure

The patterns of septation in filaments of Escherichia coli, formed as a consequence of the lack of an active ftsA gene product and then returned to permissive conditions, were analyzed in isogenic strains containing three different mutated alleles of ftsA. Septation was blocked for at least one doubling time at the potential septation sites that presumably contained inactive FtsA protein but not at those sites containing either the active gene product or no gene product at all. These results suggested a possible structural role for the ftsA gene product in the construction of the E. coli septum.

Coupling of DNA replication and cell division: sulB is an allele of ftsZ

Treatments that damage DNA in Escherichia coli result in the inhibition of cell division. This inhibition is controlled by the lexA-recA regulatory circuit and can be specifically uncoupled by the mutations sulA (sfiA) and sulB (sfiB), which map at 21 and 2 min, respectively. Presently it is thought that sulA codes for an inducible inhibitor of cell division, the expression of which is controlled directly by the lexA repressor. In this report, it is shown that sulB is an allele of ftsZ, an essential cell division gene. A sulB mutation leads to an altered ftsZ gene product which is slightly thermosensitive and has an altered mobility on polyacrylamide gels. It is suggested that the altered ftsZ gene product is resistant to the sulA inhibitor, thus permitting cell division after induction of the SOS response. It is also shown that an increase in the gene dosage of ftsZ delays the onset of filamentation after SOS induction.

Cytoplasmic steps of peptidoglycan synthesis in Escherichia coli

The cellular pool levels of most of the cytoplasmic precursors of peptidoglycan synthesis were determined for normally growing cells of Escherichia coli K-12. In particular, a convenient method for analyzing the uridine nucleotide precursor contents was developed by associating gel filtration and reverse-phase high-pressure liquid chromatography techniques. The enzymatic parameters of the four synthetases which catalyze the stepwise addition of L-alanine, D-glutamic acid, meso-diaminopimelic acid, and D-alanyl-D-alanine to uridine diphosphate-N-acetylmuramic acid were determined. It was noteworthy that the pool levels of L-alanine, D-glutamic acid, meso-diaminopimelic acid, and D-alanyl-D-alanine were much higher than the Km values determined for these substrates, whereas the molar concentrations of the uridine nucleotide precursors were lower than or about the same order of magnitude as the corresponding Km values. Taking into consideration the data obtained, an attempt was made to compare the in vitro activities of the D-glutamic acid, meso-diaminopimelic acid, and D-alanyl-D-alanine adding enzymes with their in vivo functioning, expressed by the amounts of peptidoglycan synthesized. The results also suggested that these adding activities were not in excess in the cell under normal growth conditions, but their amounts appeared adjusted to the requirements of peptidoglycan synthesis. Under the different in vitro conditions considered, only low levels of L-alanine adding activity were observed.

Identification of new genes in a cell envelope-cell division gene cluster of Escherichia coli: cell division gene ftsQ

We report the identification, cloning, and mapping of a new cell division gene, ftsQ. This gene formed part of a cluster of three division genes (in the order ftsQ ftsA ftsZ) which itself formed part of a larger cluster of at least 10 genes, all of which were involved in some step in cell division, cell envelope synthesis, or both. The ftsQAZ group was transcribed from at least two independent promoters.