Upregulation of asparagine synthetase fails to avert cell cycle arrest induced by L-asparaginase in TEL/AML1-positive leukaemic cells

L-Asparaginase is a standard component in chemotherapy of childhood acute lymphoblastic leukaemia (ALL). Leukaemic cells carrying TEL/AML1 fusion gene are more sensitive to treatment with L-asparaginase compared to other subtypes of ALL. We demonstrate in vitro the prolonged growth suppression of TEL/AML1[+] cells compared to TEL/AML1[-] leukaemic cells after L-asparaginase treatment simulating treatment protocol. Cell cycle analysis revealed TEL/AML1[+] cells to accumulate in G1/G0 phase (81-98%) compared to TEL/AML1[-] cells (47-60%). Quantitative analysis of asparagine synthetase (AsnS) expression showed the ability of TEL/AML1[+] cells to increase AsnS mRNA levels after L-asparaginase treatment to the same extent as TEL/AML1[-] leukaemic and nonleukaemic lymphoid cells. We hypothesise that TEL/AML1[+] cells are unable to progress into the S phase of cell cycle under nutrition stress caused by L-asparaginase, despite the ability of AsnS upregulation. Significantly higher expression of AsnS was found in untreated leukaemic cells from children with TEL/AML1[+] ALL (n=20) in comparison with the group of age-matched children with ALL bearing no known fusion gene (n=25; P=0.0043). Interestingly, none of the TEL/AML1[+] patients with high AsnS level relapsed, whereas 10/15 patients with AsnS below median relapsed (P=0.00028). Therefore, high AsnS levels in TEL/AML1[+] patients correlate with better prognosis, possibly reflecting the stretched metabolic demand of the lymphoblast.

Correlation of ASN2 gene expression with ammonium metabolism in Arabidopsis

In Arabidopsis, asparagine (Asn) synthetase is encoded by a small gene family (ASN1, ASN2, and ASN3). It has been shown that ASN1 and ASN2 exhibit reciprocal gene expression patterns toward light and metabolites. Moreover, changes in total free Asn levels parallel the expression of ASN1, but not ASN2. In this study, we show that ASN2 expression correlates with ammonium metabolism. We demonstrate that the light induction of ASN2 is ammonium dependent. The addition and removal of ammonium exerted fast and reciprocal effects on the levels of ASN2 mRNA, specifically under light-grown conditions. NaCl and cold stress increased cellular free ammonium and ASN2 mRNA levels in a coordinated manner, suggesting that the effects of stress on ASN2 expression may be mediated via accumulation of ammonium. The correlation between ASN2 and cellular ammonium metabolism was further demonstrated by analysis of ASN2 transgenic plants. When plants were grown on Murashige and Skoog medium containing 50 mm ammonium, ASN2 overexpressors accumulated less endogenous ammonium compared with the wild-type Colombia-0 and ASN2 underexpressors. When plants were subjected to high-light irradiance, ammonium levels built up. Under such conditions, ASN2 underexpressors accumulated more endogenous ammonium than the wild-type Colombia-0 and ASN2 overexpressors. These results support the notion that ASN2 is closely correlated to ammonium metabolism in higher plants.

Amino acids as regulators of gene expression: molecular mechanisms

Regulation of gene expression by nutrients in mammals is an important mechanism allowing them to adapt their physiological functions according to the supply of nutrient in the diet. It has been shown recently that amino acids are able to regulate by themselves the expression of numerous genes. CHOP, asparagine synthetase, and IGFBP-1 regulation following AA starvation will be described in this review with special interest in the molecular mechanisms involved.

Nodule-specific modulation of glutamine synthetase in transgenic Medicago truncatula leads to inverse alterations in asparagine synthetase expression

Transgenic Medicago truncatula plants were produced harboring chimeric gene constructs of the glutamine synthetase (GS) cDNA clones (MtGS1a or MtGS1b) fused in sense or antisense orientation to the nodule-specific leghemoglobin promoter Mtlb1. A series of transgenic plants were obtained showing a 2- to 4-fold alteration in nodule GS activity when compared with control plants. Western and northern analyses revealed that the increased or decreased levels of GS activity correlate with the amount of cytosolic GS polypeptides and transcripts present in the nodule extracts. An analysis of the isoenzyme composition showed that the increased or decreased levels of GS activity were attributable to major changes in the homo-octameric isoenzyme GS1a. Nodules of plants transformed with antisense GS constructs showed an increase in the levels of both asparagine synthetase (AS) polypeptides and transcripts when compared with untransformed control plants, whereas the sense GS transformants showed decreased AS transcript levels but polypeptide levels similar to control plants. The polypeptide abundance of other nitrogen metabolic enzymes NADH-glutamic acid synthase and aspartic acid amino-transferase as well as those of major carbon metabolic enzymes phosphoenolpyruvate carboxylase, carbonic anhydrase, and sucrose synthase were not affected by the GS-gene manipulations. Increased levels of AS polypeptides and transcripts were also transiently observed in nodules by inhibiting GS activity with phosphinothricin. Taken together, the results presented here suggest that GS activity negatively regulates the level of AS in root nodules of M. truncatula. The potential role of AS in assimilating ammonium when GS becomes limiting is discussed.

Synthesis and characterization of an N-acylsulfonamide inhibitor of human asparagine synthetase

[structure: see text] The synthesis of N-acylsulfonamide 6, which is an analogue of beta-aspartyl-AMP, is described. This compound appears to be the first and only potent inhibitor of human asparagine synthetase that has been described to date. The N-acylsulfonamide 6 exhibits slow-onset inhibition kinetics, with a K(i) of 728 nM. Preparation and characterization of two additional N-acylsulfonamide analogues has also demonstrated the importance of hydrogen-bonding interactions in the recognition of the AS inhibitor with the enzyme. These observations provide the basis for the discovery of new compounds with application in the treatment of drug-resistant leukemia.

Characterization of the nutrient-sensing response unit in the human asparagine synthetase promoter

Transcription from the human asparagine synthetase (A.S.) gene is increased in response to either amino acid (amino acid response) or glucose (endoplasmic reticulum stress response) deprivation. These two independent nutrient-sensing pathways converge on the same set of genomic cis -elements, referred to as nutrient sensing-response elements (NSREs) 1 and 2, within the A.S. promoter. The present report uses single-nucleotide mutagenesis to confirm that both NSRE-1 and NSRE-2 are absolutely required for gene activation and to identify the boundaries of each binding site. The core sequence of the NSRE-1 site is contained within nucleotides -68 to -60 and the NSRE-2 core sequence is within nucleotides -48 to -43. Through insertion or deletion of 5-10 nucleotides in the intervening sequence between NSRE-1 and NSRE-2, transient transfection studies with an A.S. promoter/reporter gene construct showed that the 11 bp distance between these two elements is critical. These results document that the optimal configuration is with both binding sites on the same side of the DNA helix, only one helical turn away from each other and the data provide support for the hypothesis that a larger multi-protein complex exists between the binding proteins for NSRE-1 and NSRE-2. The data also illustrate that the combination of NSRE-1 and NSRE-2, referred to as the nutrient-sensing response unit (NSRU), has enhancer activity in that it functions in an orientation- and position-independent manner, and conveys nutrient-dependent transcriptional control to a heterologous promoter.

Revisiting the steady state kinetic mechanism of glutamine-dependent asparagine synthetase from Escherichia coli

Escherichia coli asparagine synthetase B (AS-B) catalyzes the formation of asparagine from aspartate in an ATP-dependent reaction for which glutamine is the in vivo nitrogen source. In an effort to reconcile several different kinetic models that have been proposed for glutamine-dependent asparagine synthetases, we have used numerical methods to investigate the kinetic mechanism of AS-B. Our simulations demonstrate that literature proposals cannot reproduce the glutamine dependence of the glutamate/asparagine stoichiometry observed for AS-B, and we have therefore developed a new kinetic model that describes the behavior of AS-B more completely. The key difference between this new model and the literature proposals is the inclusion of an E.ATP.Asp.Gln quaternary complex that can either proceed to form asparagine or release ammonia through nonproductive glutamine hydrolysis. The implication of this model is that the two active sites in AS-B become coordinated only after formation of a beta-aspartyl-AMP intermediate in the synthetase site of the enzyme. The coupling of glutaminase and synthetase activities in AS is therefore different from that observed in all other well-characterized glutamine-dependent amidotransferases.

The mechanism for transcriptional activation of the human ATA2 transporter gene by amino acid deprivation is different than that for asparagine synthetase

After amino acid deprivation, the mRNA content for both asparagine synthetase (AS) and the system A transporter ATA2 is increased. The purpose of the reported experiments was to characterize the molecular mechanism for the ATA2 gene and to contrast the ATA2 regulatory characteristics with those of AS. Amino acid limitation was initiated by incubation of HepG2 human hepatoma cells in either amino acid-free Krebs-Ringer bicarbonate buffer or culture medium lacking the single amino acid histidine. For ATA2, like AS, the elevated mRNA content was due to increased transcription. However, there were fundamental differences between the mechanisms for nutrient regulation of the AS and ATA2 genes. When cells were deprived of amino acids, there was a lag period of approximately 4 h before an increase in AS mRNA occurred, whereas the elevation of ATA2 mRNA was readily detectable at 2-4 h. Consistent with these observations, de novo protein synthesis was absolutely required for the activation of the AS gene, but the increase in ATA2 mRNA was largely independent of protein synthesis. Furthermore, in contrast to AS, transcription from the ATA2 gene was not increased by glucose deprivation. Given this lack of ATA2 transcriptional activation by glucose starvation and that the induction of the AS gene by glucose or amino acid starvation is mediated by common genomic elements, it is likely that the ATA2 gene does not contain the same genomic amino acid-responsive cis-elements as the AS gene.

Effect of lignins and their precursors on nitric oxide, citrulline and asparagine production by mouse macrophage-like Raw 264.7 cells

Lignins, tannins and flavonoids are commonly found polyphenols. Among these polyphenols, lignins, polymers of phenylpropenoids complexed with polysaccharides, were the least cytotoxic and most potently stimulated the production of nitric oxide (NO), citrulline and asparagine by mouse macrophage-like Raw 264.7 cells. The maximum production of these substances reached the level attained by lipopolysaccharide (LPS). However, epigallocatechin gallate, phenylpropenoid monomers (ferulic acid, caffeic acid) and gallic acid (component unit of tannin) were inactive. These data suggest that the macrophage-stimulation activity of polyphenols depends, at least in part, on their molecular weight or structural configuration. There was a positive relationship between the extent of asparagine production and that of NO or citrulline. Western blot analysis demonstrated that both lignins and LPS elevated the cellular level of asparagine synthetase. The present study suggests the possible link between the stimulated asparagine production and macrophage activation.

Channeling of substrates and intermediates in enzyme-catalyzed reactions

The three-dimensional structures of tryptophan synthase, carbamoyl phosphate synthetase, glutamine phosphoribosylpyrophosphate amidotransferase, and asparagine synthetase have revealed the relative locations of multiple active sites within these proteins. In all of these polyfunctional enzymes, a product formed from the catalytic reaction at one active site is a substrate for an enzymatic reaction at a distal active site. Reaction intermediates are translocated from one active site to the next through the participation of an intermolecular tunnel. The tunnel in tryptophan synthase is approximately 25 A in length, whereas the tunnel in carbamoyl phosphate synthetase is nearly 100 A long. Kinetic studies have demonstrated that the individual reactions are coordinated through allosteric coupling of one active site with another. The participation of these molecular tunnels is thought to protect reactive intermediates from coming in contact with the external medium.

An alternative mechanism for the nitrogen transfer reaction in asparagine synthetase

In the absence of crystallographic data, the mechanism of nitrogen transfer from glutamine in asparagine synthetase (AS) remains under active investigation. Surprisingly, the glutamine-dependent AS from Escherichia coli (AsnB) appears to lack a conserved histidine residue, necessary for nitrogen transfer if the reaction proceeds by the accepted pathway in other glutamine amidotransferases, but retains the ability to synthesize asparagine. We propose an alternative mechanism for nitrogen transfer in AsnB which obviates the requirement for participation of histidine in this step. Our hypothesis may also be more generally applicable to other glutamine-dependent amidotransferases.

Synthesis of L-4,4-difluoroglutamic acid via nucleophilic addition to a chiral aldehyde

Fluorine-containing derivatives of amino acids are assuming increasing importance as probes of biological function and enzyme mechanism. We now report a new, flexible route to enantiomerically pure L-4,4-difluoroglutamic acid that exploits the addition of difluorinated nucleophiles to configurationally stable alpha-aminoaldehydes. Conversion of the difluorinated adducts to L-4,4-difluoroglutamic acid can be accomplished in three steps by Barton-McCombie dehydroxylation and acid hydrolysis.

Hypermethylation of CpG islands in the mouse asparagine synthetase gene: relationship to asparaginase sensitivity in lymphoma cells. Partial methylation in normal cells

We have sequenced the promoter region of the murine asparagine synthetase gene and examined its methylation profile in the CpG islands of L-asparaginase-sensitive 6C3HED cells (asparagine auxotrophs) and resistant variants (prototrophs). In the former, complete methylation of the CpG island is correlated with failure of expression of mRNA: cells of the latter possess both methylated and unmethylated alleles, as do cells of the intrinsically asparagine-independent lines L1210 and EL4. A similar phenomenon was seen in normal splenic cells of adult mice. This was age related: no methylation was found in weanlings, but up to 45% of gene copies in animals 18 weeks or older were methylated. It was also tissue related, with methylation occurring rarely in liver cells. The relationship of these changes to oncogenesis is considered.

Recent advances on molecular mechanisms involved in amino acid control of gene expression

In mammals, the impact of nutrients on gene expression has become an important area of research. Because amino acids have multiple and important functions, their homeostasis has to be finely maintained. However, amino acidaemia can be affected by certain nutritional conditions or various forms of aggression. It follows that mammals have to adjust several of their physiological functions involved in the adaptation to amino acid availability by regulating the expression of numerous genes. It has been shown that amino acids by themselves can modify the expression of target genes. However, the current understanding of amino acid-dependent control of gene expression has just started to emerge. This review focuses on the recent advances on mechanisms involved in the amino acids control of gene expression. Several examples discussed in this paper demonstrate that amino acids regulate gene expression at the level of transcription, messenger RNA stability and translation.

Multiple adaptive mechanisms affect asparagine synthetase substrate availability in asparaginase-resistant MOLT-4 human leukaemia cells

Childhood acute lymphoblastic leukaemia is treated by combination chemotherapy with a number of drugs, almost always including the enzyme L-asparaginase (ASNase). Although the initial remission rate is quite high, relapse and associated drug resistance remain a problem. In vitro studies have demonstrated an adaptive increase in asparagine synthetase (AS) expression in ASNase-resistant cells, which is believed to permit ASNase-resistant human leukaemia cells to survive in vivo. The present results, obtained with ASNase-sensitive and -resistant human MOLT-4 leukaemia cell lines, illustrate that several other adaptive processes occur to provide sufficient amounts of the AS substrates, aspartate and glutamine, required to support this increased enzymic activity. In both cell populations, aspartate is derived almost exclusively from intracellular sources, whereas the necessary glutamine arises from both intracellular and extracellular sources. Transport of glutamine into ASNase-resistant cells is significantly enhanced compared with the parental cells, whereas amino acid efflux (e.g. asparagine) is reduced. Most of the adaptive change for the amino acid transporters, Systems A, ASC and L, is rapidly (12 h) reversed following ASNase removal. The enzymic activity of glutamine synthetase is also enhanced in ASNase-resistant cells by a post-transcriptional mechanism. The results demonstrate that there are several sites of metabolic adaptation in ASNase-treated leukaemia cells that serve to promote the replenishment of both glutamine and asparagine.

Asparagine synthetase expression alone is sufficient to induce l-asparaginase resistance in MOLT-4 human leukaemia cells

Childhood acute lymphoblastic leukaemia (ALL) is treated by combination chemotherapy with a number of drugs, always including the enzyme L-asparaginase (ASNase). Although the initial remission rate is quite high, relapse and associated drug resistance are a significant problem. In vitro studies have demonstrated increased asparagine synthetase (AS) expression in ASNase-resistant cells, which has led to the hypothesis that elevated AS activity permits drug-resistant survival. The data presented show that not only is elevated AS expression a property of ASNase-resistant MOLT-4 human leukaemia cells, but that short-term (12 h) treatment of the cells with ASNase causes a relatively rapid induction of AS expression. The results also document that the elevated expression of AS in ASNase-resistant cells is not fully reversible, even 6 weeks after ASNase removal from the culture medium. Furthermore, ASNase resistance, assessed as both drug-insensitive cell growth rates and decreased drug-induced apoptosis, parallels this irreversible AS expression. Mimicking the elevated AS activity in ASNase-resistant cells by overexpression of the human AS protein by stable retroviral transformation of parental MOLT4 cells is sufficient to induce the ASNase-resistance phenotype. These data document that ASNase resistance in ALL cells is a consequence of elevated AS expression and that although other drug-induced metabolic changes occur, they are secondary to the increased asparagine biosynthetic rate.

Cloning, characterization and mRNA expression analysis of PVAS1, a type I asparagine synthetase gene from Phaseolus vulgaris

A gene encoding a putative asparagine synthetase (AS; EC 6.3.5.4) has been isolated from common bean (Phaseolus vulgaris L.). A 2-kb cDNA clone of this gene (PVAS1) encodes a protein of 579 amino acids with a predicted molecular mass of 65,265 Da, an isoelectric point of 6.3, and a net charge of -9.3 at pH 7.0. The PVAS1 protein sequence conserves all the amino acid residues that are essential for glutamine-dependent AS, and PVAS1 complemented an Escherichia coli asparagine auxotroph, which demonstrates that it encodes a glutamine-dependent AS. The PVAS1 protein showed the highest similarity to soybean SAS1, and piled up with other legume ASs to form an independent dendritic group of type-I AS enzymes. Northern blot analyses revealed that the expression pattern of PVAS1 resembles that of PVAS2, another AS previously described in the common bean. Unlike PVAS2, however, PVAS1 was not expressed in the nodule and was not repressed by light, suggesting different functions for these two AS genes.

Metabolite and light regulation of metabolism in plants: lessons from the study of a single biochemical pathway

We are using molecular, biochemical, and genetic approaches to study the structural and regulatory genes controlling the assimilation of inorganic nitrogen into the amino acids glutamine, glutamate, aspartate and asparagine. These amino acids serve as the principal nitrogen-transport amino acids in most crop and higher plants including Arabidopsis thaliana. We have begun to investigate the regulatory mechanisms controlling nitrogen assimilation into these amino acids in plants using molecular and genetic approaches in Arabidopsis. The synthesis of the amide amino acids glutamine and asparagine is subject to tight regulation in response to environmental factors such as light and to metabolic factors such as sucrose and amino acids. For instance, light induces the expression of glutamine synthetase (GLN2) and represses expression of asparagine synthetase (ASN1) genes. This reciprocal regulation of GLN2 and ASN1 genes by light is reflected at the level of transcription and at the level of glutamine and asparagine biosynthesis. Moreover, we have shown that the regulation of these genes is also reciprocally controlled by both organic nitrogen and carbon metabolites. We have recently used a reverse genetic approach to study putative components of such metabolic sensing mechanisms in plants that may be conserved in evolution. These components include an Arabidopsis homolog for a glutamate receptor gene originally found in animal systems and a plant PII gene, which is a homolog of a component of the bacterial Ntr system. Based on our observations on the biology of both structural and regulatory genes of the nitrogen assimilatory pathway, we have developed a model for metabolic control of the genes involved in the nitrogen assimilatory pathway in plants.

Development of a double-drug-resistant human leukemia model to cytosine arabinoside and L-asparaginase: evaluation of cross-resistance to other treatment modalities

We have developed an in vitro model of 38 T-lymphoblastic leukemia lines resistant to cytosine arabinoside (ara-C) and L-asparaginase (ASNase). Of these, 26 cell lines resistant to both drugs, 6 resistant to ara-C, and 6 resistant to ASNase were isolated. In 18 of these cell lines, all randomly selected, resistance to ara-C, ASNase and gamma radiation was documented by the MTT and trypan blue assays, as well as flow cytometry with Annexin V and propidium iodide (PI) staining. In these lines, p53, p21WAF1, and bcl-2 levels were measured by ELISA. Results show that P21WAF1 upregulation following p53 induction did not occur, suggesting that p53 function may be lost. Moreover, the data imply that upregulation of bcl-2 is critical in the development of resistance to ara-C and ASNase in these leukemic lines. In the CEM/0 parent line, p53 maintained its ability to interact with its DNA binding site as documented by the electrophoretic mobility shift assay (EMSA). But in one single- and one double-resistant leukemic cell line examined, p53 was not shown to maintain this ability. We conclude that double-resistant clones to ara-C and ASNase are refractory to both drugs, providing an excellent leukemic model to investigate the multiple-drug resistance.

Organ and cellular localization of asparagine synthetase in rice plants

DNA gel blot analysis suggested that asparagine synthetase (AS; EC 6.3.5.4) occurred as a single gene in rice. A fusion protein consisting of 17 kDa tagged-region from pET32a(+) expression plasmid and 42 kDa N-terminal region of rice AS was first expressed in Escherichia coli. The resulting polypeptide was purified and a mono-specific antibody for rice AS was prepared after affinity-purification with the antigen. Immunoblotting revealed a high content of AS protein in the leaf sheath at the second position from the fully expanded top leaf and in grains at the middle stage of ripening. Accumulation of mRNA for AS was also observed in these organs. During the ripening of the spikelets, the AS protein contents increased during the first 21 days after flowering, then declined rapidly. Immunolocalization analysis revealed signals for AS protein in the companion cells of vascular bundles of leaf sheath and phloem-parenchyma cells, nucellar projection, and nucellar epidermis of dorsal vascular bundles of grains.

Evidence for multiple signaling pathways in the regulation of gene expression by amino acids in human cell lines

In mammals, plasma concentrations of amino acids (AA) are affected by nutritional or pathologic conditions. Alterations in AA profiles have been reported as a result of a deficiency of any one of the essential AA, a dietary imbalance of AA or an insufficient intake of protein. In recent years, evidence has accumulated that AA availability regulates the expression of several genes involved in the regulation of a number of cellular functions or AA metabolism. Nevertheless, the molecular mechanisms involved in the AA regulation of mammalian gene expression are limited, particularly the signaling pathways mediating the AA response. This work provides a better understanding of the signaling pathways involved in the AA control of gene expression. We studied the expression of C/EBP homologous protein (CHOP) and asparagine synthetase (AS) in response to deprivation of a single AA and investigated the possible link between protein synthesis inhibition due to amino acid limitation and gene expression. We have shown the following: 1) several mechanisms are involved in the AA control of gene expression. When omitted from the culture medium, each AA can activate one (or several) specific signaling pathways leading to the regulation of one specific pattern of genes. 2) AA limitation by itself can induce gene expression independently of a cellular stress due to protein synthesis inhibition. Together, these results suggest that AA control of gene expression involves several specific mechanisms by which one AA (or one group of AA) can activate one signaling pathway and thus alter one specific pattern of gene expression.

Measuring asparagine synthetase activity in crude plant extracts

Asparagine synthetase B (AS) is the primary enzyme responsible for asparagine synthesis in plants. Routine biochemical studies of this enzyme's activity have been hindered by several problems including enzyme instability and rapid physiological turnover, endogenous inhibitors, competing pathways, and asparaginase activity. We describe an extraction procedure and assay conditions that provide a reliable, direct assay for the determination of AS activity in crude plant extracts. This assay performed well with several leguminous species and the enzyme preparation retained activity for up to 3 weeks when stored at -80 degrees C. Radio-HPLC detection enabled quantitative measurement of de novo aspargine synthesis in the extracts. Optimal activity was obtained with 1 mM glutamine and 10 mM ATP in the reaction assay. Aminooxyacetic acid (AOA, 1 mM) which prevents the assimilation of aspartate into the TCA cycle, was necessary to measure AS activity in peas, but not in lupine or soybean.

A mutation in the Corynebacterium glutamicum ltsA gene causes susceptibility to lysozyme, temperature-sensitive growth, and L-glutamate production

The Corynebacterium glutamicum mutant KY9714, originally isolated as a lysozyme-sensitive mutant, does not grow at 37 degrees C. Complementation tests and DNA sequencing analysis revealed that a mutation in a single gene of 1,920 bp, ltsA (lysozyme and temperature sensitive), was responsible for its lysozyme sensitivity and temperature sensitivity. The ltsA gene encodes a protein homologous to the glutamine-dependent asparagine synthetases of various organisms, but it could not rescue the asparagine auxotrophy of an Escherichia coli asnA asnB double mutant. Replacement of the N-terminal Cys residue (which is conserved in glutamine-dependent amidotransferases and is essential for enzyme activity) by an Ala residue resulted in the loss of complementation in C. glutamicum. The mutant ltsA gene has an amber mutation, and the disruption of the ltsA gene caused lysozyme and temperature sensitivity similar to that in the KY9714 mutant. L-Glutamate production was induced by elevating growth temperature in the disruptant. These results indicate that the ltsA gene encodes a novel glutamine-dependent amidotransferase that is involved in the mechanisms of formation of rigid cell wall structure and in the L-glutamate production of C. glutamicum.