Activation of transcription of hut DNA by glutamine synthetase

Regulation of Rhizobium nitrogen fixation by the unadenylylated glutamine synthetase I system

Rhizobium sp. 32H1 glutamine auxotrophs have a complex phenotype: a highly adenylylated glutamine synthetase [GS; L-glutamate:ammonia ligase (ADP-forming), EC 6.3.1.2] I and an undetectable GS II (GS II(-)). They are defective in the adenylylation cascade system for GS I. Prototrophic revertants are of two classes: those (3204 type) which retain the adenylylated GS I phenotype but become GS II(+), and those (3205 type) which acquire a constitutive unadenylylated GS I but remain GS II(-). Like the parent auxotroph, 3204 remains incapable of nitrogen fixation both in culture and in root nodules of Macroptileum atropurpureum. In contrast, 3205 is nitrogenase constitutive. This implies that GS I or associated adenylylation proteins are involved in the control of Rhizobium 32H1 nif gene expression and that GS II is not so involved. Normally, rhizobia fix atmospheric N(2) only during symbiosis and, in so doing, only transiently synthesize nitrogenase. Moreover, whereas wild-type strains export ammonium, constitutive strains can assimilate ammonium produced by nitrogenase. This phenotype allows direct selection of nitrogen fixation-defective mutants in Rhizobium.

Nitrogen metabolism in Aspergillus parasiticus NRRL 3240 and A. flavus NRRL 3537 in relation to aflatoxin production

The relationship between nitrogen assimilation, metabolism and aflatoxin formation has been investigated in a toxigenic and a non-toxigenic strain of Aspergillus parasiticus. Ammonia from the medium is mainly assimilated via NADP-requiring glutamate dehydrogenase. During growth NAD-requiring glutamate dehydrogenase followed an inverse pattern of activity with respect to NADP glutamate dehydrogenase. Alpha-ketoglutarate, the product of NAD glutamate dehydrogenase, stimulated acetate incorporation into aflatoxins. Glutamine synthetase, ornithine transcarbamylase, both utilizing glutamate as substrate were assayed under different growth conditions. An important regulatory role for glutamine synthetase is suggested. The metabolic route of asparagine utilization was also investigated. Both the known pathways, glutamate oxaloacetate transaminase and glutamate pyruvate transaminase are operative simultaneously.

Control of utilization of L-arginine, L-ornithine, agmatine, and putrescine as nitrogen sources in Escherichia coli K-12

The regulation of the synthesis of the enzymes involved in the utilization of L-arginine, L-ornithine, agmatine, and putrescine as a sole nitrogen source in Escherichia coli K-12 was examined. The synthesis of agmatine ureohydrolase, putrescine aminotransferase, and pyrroline dehydrogenase is dually controlled by catabolite repression and nitrogen availability. Catabolite repression of agmatine ureohydrolase, but not that of putrescine aminotransferase or pyrroline dehydrogenase, is relieved by the addition of cAMP. Agmatine ureohydrolase synthesis in addition is subject to induction by L-arginine and agmatine. Arginine decarboxylase and ornithine decarboxylase synthesis is not sensitive to catabolite repression or to stimulation by nitrogen limitation or subject to substrate induction.

Expression of Klebsiella pneumoniae nif genes in Proteus mirabilis

Self-transmissible plasmids carrying his and nif genes from Klebsiella pneumoniae have been introduced into three his mutants of Proteus mirabilis: strains 5006-1, WR19 and WR20. Expression of his by the transconjugants was unequivocal, if slightly temperature-sensitive, but none was Nif+ when tested for acetylene reduction in anaerobic glucose medium using inocula from rich or glucose-minimal aerobic agar cultures. Succinate or pyruvate in place of glucose, low glucose, lower temperature or elevated Na2MoO4 did not allow nif expression and no nitrogenase MoFe-protein peptide was detected immunologically after exposure to conditions in which diazotrophic enterobacteria, normal or genetically constructed, derepress nif. One strain, P. mirabilis WR19, carrying the his nif Kmr plasmid pMF250 was examined in detail. The nif activator gene nifA was introduced on the plasmid pCK1. Such derivatives remained Nif- when tested, after aerobic growth on rich agar media, with normal or low glucose, with succinate or with elevated Mo. However, pre-conditioning by aerobic growth on glucose-minimal agar led to subsequent anaerobic expression of nif in glucose medium from pMF250 in WR19 carrying pCK1. NH+4 or proline could serve as N-source in the glucose-minimal agar. Maximum activity was about 5% of that of K. pneumoniae in our assay conditions. Material cross-reacting with anti-serum to the nitrogenase MoFe protein was formed. Nitrogenase activity was not 'switched off' by NH+4. P. mirabilis WR19 (pCK1) showed NH+4-constitutive temperature-sensitive kanamycin resistance (a nif-related phenotype of this plasmid) in aerobic glucose minimal medium.(ABSTRACT TRUNCATED AT 250 WORDS)

Regulation of hutUH operon expression by the catabolite gene activator protein-cyclic AMP complex in Klebsiella aerogenes

RNA polymerase transcribed the hutUH operon of Klebsiella aerogenes if the catabolite gene activator protein (CAP) and cyclic AMP (cAMP) were present or if the DNA template was derived from a promoter mutant in which hutUH expression was independent of the need for positive effectors. In the absence of CAP or cAMP, not only was hutUH transcription absent, but transcription in the opposite direction (toward hutC) was initiated at a site (pC) ca. 70 base pairs from the site (pUH) of hutUH mRNA initiation. When the pC promoter was cloned in front of a promoterless galK gene, active expression of galK was observed. Thus, the pC promoter is active in vivo as well as in vitro. Transcription from pUH and pC may be mutually exclusive, with the major effect of CAP and cAMP being to prevent transcription from pC, thus relieving the antagonistic effect on transcription from pUH. This "double-negative" control by CAP-cAMP is supported by two observations: (i) CAP-cAMP was unable to activate transcription from pUH if RNA polymerase had been previously bound to pC and (ii) a mutation that allowed transcription from pUH in the absence of positive effectors simultaneously eliminated the activity of pC. An alternative model, in which CAP-cAMP is required for pUH expression and RNA polymerase binding at pC serves to modulate this control in some unknown way, is also considered. The physiological role of the transcript from pC other than regulation of pUH is unknown.

Cloning of the glnA, ntrB and ntrC genes of Klebsiella pneumoniae and studies of their role in regulation of the nitrogen fixation (nif) gene cluster

The glnA, ntrB and ntrC genes of Klebsiella pneumoniae have been cloned, on a 12 kb HindIII fragment, into the plasmid pACYC184. In a coupled in vitro transcription/translation system the resultant plasmid, pGE100, directed synthesis of five polypeptides (molecular weights 73, 53, 51, 39, 36 kd) from the cloned fragment. A number of plasmids were derived from pGE100 and studied by complementation analysis and in vitro transcription/translation in order to locate particular genes and identify their products. On the basis of the results presented here, together with previous genetic and physical characterisation of the glnA gene and its product in other enteric bacteria, we propose that the 53 kd polypeptide is the glnA gene product (glutamine synthetase monomer). Two polypeptides (36 kd and 51 kd) were synthesised from a 3 kb region previously defined as glnR. In E. coli and S. typhimurium this region comprises two genes ntrB and ntrC with products of 36 kd and 54 kd respectively. This analogy supports the idea that the 36 kd and 51 kd polypeptides are the products of the K. pneumoniae ntrB and ntrC genes respectively. Comparison of these assignments with the physical map of the region indicates a gene order glnA, ntrB, ntrC. Assessment of the Nif phenotype of a glnA-ntrC deletion strain carrying various clones from pGE100 demonstrated that glnA is not required for expression of the nif regulon and that of the three genes cloned, ntrC alone is sufficient for nif expression.

The mode of genetic transmission of gouty family with increased phosphoribosylpyrophosphate synthetase activity

The mode of genetic transmission of gout and increased activity of phosphoribosylphrophosphate synthetase (PRPPS) was studied in one family. Among 15 members of Family F, two male members had gout and had PRPPS activity of erythrocyte lysates three times higher than normal subjects. Five female members had activity 2.5 times higher than normal. The difference between the activities of male and female affected members was statistically significant (P less than 0.05). To examine the genetic trait of this abnormal PRPPS, the incorporation of 3H-adenine into erythrocytes or lymphocytes was studied using autoradiography. The number of grains which show the uptake of labeled adenine into cells revealed a normal distribution pattern in two normal persons and in two male patients, and a mixed pattern of the two cell populations in two female affected members. These results suggested mosaicism in female members and X-linked dominant transmission of this trait. Thermal inactivation of PRPPS of an affected female was intermediate between that from a normal subject and that from the affected males. This result showed the heterogeneity of the PRPPS from the hemolysate of an affected female. The genotype of PRPPS on the X-chromosome was assumed and the lod score between PRPPS and Xg was also estimated. From these findings and electrophoretical study, it was suggested that the abnormal enzyme was a mutant enzyme transmitted in an X-linked dominant trait, and that the mutation occurred on the structural gene of the PRPPS.

Regulation of expression from the glnA promoter of Escherichia coli in the absence of glutamine synthetase

One of the suspected regulators of glutamine synthetase [L-glutamate:ammonia ligase (ADP-forming), EC 6.3.1.2] in enteric bacteria is glutamine synthetase itself. We isolated Escherichia coli strains carrying fusions of the beta-galactosidase structural gene to the promoter of the glutamine synthetase gene, with the aid of the Casadaban Mud1 (ApR, lac, cts62) phage. Some aspects of regulation were retained in haploid fusion strains despite the absence of glutamine synthetase, whereas other aspects required glutamine synthetase catalytic or regulatory activity or both. The direction of transcription of the glutamine synthetase gene was also determined.

Regulation of nitrogen metabolism in glutamine auxotrophs of Klebsiella pneumoniae

We examined the regulation of nitrogen metabolism in four classes (glnA, glnB, glnF, and glnG) of Gln- auxotrophs of Klebsiella pneumoniae. These studies indicate that glutamine synthetase does not directly mediate the physiological response to NH4+ in this organism. We present evidence suggesting that the effect of NH4+ on the expression of genes involved in nitrogen metabolism involves the products of the glnF and glnG genes.

Purification of glutamine synthetase from a variety of bacteria

We have developed two procedures which allow the very rapid purification of glutamine synthetase (GS) from a diverse variety of bacteria. The first procedure, based upon differential sedimentation, depends upon the association of GS with deoxyribonucleic acid in cell extracts. The second procedure, derived from the method of C. Gross et al (J. Bacteriol. 128:382-389, 1976) for purifying ribonucleic acid polymerase by polyethylene glycol (PEG) precipitation, enabled us to obtain high yields of GS from either small or large quantities of cells. We used the PEG procedure to purify GS from Klebsiella aerogenes, K. pneumoniae, Escherichia coli, Salmonella typhimurium, Rhizobium sp. strain 32H1, R. meliloti, Azotobacter vinelandii, Pseudomonas putida, Caulobacter crescentus, and Rhodopseudomonas capsulata. The purity of the GS obtained, judged by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, was high, and in many instances only a single protein band was detected.

Isolation of Klebsiella aerogenes mutants cis-dominant for glutamine synthetase expression

We have isolated three strains of Klebsiella aerogenes that failed to show repression of glutamine synthetase even when grown under the most repressing conditions for the wild-type strain. These mutant strains were selected as glutamine-independent derivatives of a strain that is merodiploid for the glnA region and contains a mutated glnF allele. The mutation responsible for the Gln+ phenotype in each strain was tightly linked to glnA, the structural gene for glutamine synthetase, and was dominant to the wild-type allele. These mutations are probably lesions in the control region of the glnA gene, since each mutation was cis-dominant for constitutive expression of the enzyme in hybrid merodiploid strains. Strains harboring this class of mutations were unable to produce a high level of glutamine synthetase unless they also contained an intact glnF gene, and unless cells were grown in derepressing medium. This study supports the idea that the glnA gene is regulated both positively and negatively, and that the deoxyribonucleic acid sites critical for positive control and negative control are functionally distinct.

Regulation of Klebsiella pneumoniae hut operons by oxygen

We investigated the regulation of genes concerned with nitrogen metabolism by oxygen in the facultative anaerobe Klebsiella pneumoniae. We found oxygen to be required for the expression of the hut operons; the effect of O2 on the glutamine synthetase and urease was less pronounced than on the hut operons. Glutamine synthetase was transiently repressed during the transition from an aerobic to an anaerobic environment. Regulation of hut by O2 suppressed the effect of nitrogen limitation on the expression of these genes.

The enzymes of the ammonia assimilation in Pseudomonas aeruginosa

Glutamine synthetase from Pseudomonas aeruginosa is regulated by repression/derepression of enzyme synthesis and by adenylylation/deadenylylation control. High levels of deadenylylated biosynthetically active glutamine synthetase were observed in cultures growing with limiting amounts of nitrogen while synthesis of the enzyme was repressed and that present was adenylylated in cultures with excess nitrogen. NADP- and NAD-dependent glutamate dehydrogenase could be separated by column chromatography and showed molecular weights of 110,000 and 220,000, respectively. Synthesis of the NADP-dependent glutamate dehydrogenase is repressed under nitrogen limitation and by growth on glutamate. In contrast, NAD-dependent glutamate dehydrogenase is derepressed by glutamate. Glutamate synthase is repressed by glutamate but not by excess nitrogen.

Glutamine synthetase mutations which affect expression of nitrogen fixation genes in Klebsiella pneumoniae

Previous studies have implicated glutamine synthetase (L-glutamate:ammonia ligase [adenosine diphosphate for-ing], EC 6.6.1.2) as a major controlling element of the nitrogen fixation (nif) genes in Klebsiella pneumoniae. We report here the isolation of a new class of K. pneumoniae mutants which exhibit altered patterns of nif and hut (histidine utlization) regulation. The expression of nif in these mutants, which were isolated as Gln+ (glutamine nonrequiring) revertants of a particular glnA mutation, is extremely sensitive to ammonia repression. These mutants have a Nif- Hut- phenotype at external ammonia concentrations at which wild-type strains are Nif+ Hut+. On the other hand, these mutants can be fully derepressed for nif at very low ammonia concentrations. We adopted the nomenclature "GlnR- (Nif- Hut-)" to facilitate discussion of the phenotype of these mutant strains. The mutations in these strains which confer the GlnR- phenotype map at or near glnA, the structural gene for glutamine synthetase.

Nitrogen control of Salmonella typhimurium: co-regulation of synthesis of glutamine synthetase and amino acid transport systems

Nitrogen control in Salmonella typhimurium is not limited to glutamine synthetase but affects, in addition, transport systems for histidine, glutamine, lysine-arginine-ornithine, and glutamate-aspartate. Synthesis of both glutamine synthetase and transport proteins is elevated by limitation of nitrogen in the growth medium or as a result of nitrogen (N)-regulatory mutations. Increases in the amounts of these proteins were demonstrated by direct measurements of their activities, by immunological techniques, and by visual inspection of cell fractions after gel electrophoresis. The N-regulatory mutations are closely linked on the chromosome to the structural gene for glutamine synthetase, glnA: we discuss the possibility that they lie in a regulatory gene, glnR, which is distinct from glnA. Increases in amino acid transport in N-regulatory mutant strains were indicated by increased activity in direct transport assays, improved growth on substrates of the transport systems, and increased sensitivity to inhibitory analogs that are trnasported by these systems. Mutations to loss of function of individual transport components (hisJ, hisP, glnH, argT) were introduced into N-regulatory mutant strains to determine the roles of these components in the phenotype and transport behavior of the strains. The structural gene for the periplasmic glutamine-binding protein, glnH, was identified, as was a gene argT that probably encodes the structure of the lysine-arginine-ornithine-binding protein. Genes encoding the structures of the histidine- and glutamine-binding proteins are not linked to glnA or to each other by P22-mediated transduction; thus, nitrogen control is exerted on several unlinked genes.

Relation between the adenylylation state of glutamine synthetase and the expression of other genes involved in nitrogen metabolism

We have partially characterized the biochemical parameters of glutamine synthetase from Klebsiella pneumoniae and have shown that the differential affinity of adenylylated and unadenylylated glutamine synthetase for adenosine diphosphate provides a convenient means of determining the adenylylation state. Using this assay procedure, we examined the relationship between the adenylylation state and the expression of other genes involved in nitrogen assimilation. We observed no correlation between the adenylylation state and the expression of histidase, glutamine synthetase, glutamate synthase, glutamate dehydrogenase, and urease in aerobic cultures.

Role of the dsdC activator in regulation of D-serine deaminase synthesis

The activator of the D-serine deaminase operon, the product of the dsdC gene, has been partially purified. It is reasonably stable to routine purification procedures in the presence of its ligand D-serine, but not in its absence. It loses activity upon dialysis in amino acid-free buffer, but activity is completely restored upon readdition of D-serine. It apparently functions purely as an activator, no repressor function could be demonstrated at suboptimal D-serine concentration. It is a transcriptional control element. The time required for in vitro transcription of D-serine deaminase mRNA, nearly 4 min, is similar to that for beta-galactosidase. Since the beta-galactosidase monomer is a much protein, this is surprisingly long.

Role of small molecules in regulation of D-serine deaminase synthesis

Cyclic AMP is required for optimal synthesis of D-serine deaminase synthesis from dsdO+ templates and for optimal hyperinducible synthesis from low constitutive dsdO templates both in vitro and in vivo. Neither D-serine, cyclic AMP, nor dsdC activator has an effect on expression of a high constitutive dsdO template. The synthesis of the dsdC activator itself in vitro is independent of cyclic AMP. Guanosine tetraphosphate does not have a significant effect on in vitro D-serine deaminase synthesis from dsdO+ or dsdO templates. A previously described class of dsdO mutants showing partial catabolite sensitivity of constitutive D-serine deaminase synthesis proved to be low dsdO types. They all contain a low constitutive dsdC mutation; the two effects are additive with regard to level of constitutivity, but only that portion of synthesis attributable to the dsdC mutation is cyclic AMP dependent.

Specificity and regulation of gamma-aminobutyrate transport in Escherichia coli

A specific gamma-aminobutyrate (GABA) transport system in Escherichia coli K-12 cells with a K(m) of 12 muM and a V(max) of 278 nmol/ml of intracellular water per min is described. Membrane vesicles contained d-lactate-dependent activity of the system. Mutants defective in GABA transport were isolated; they lost the ability to utilize GABA as a nitrogen source, although the activities of glutamate-succinylsemialdehyde transaminase (GSST) (EC 2.6.1.19) and succinylsemialdehyde dehydrogenase (SSDH) (EC 1.2.1.16), the enzymes that catalyze GABA utilization, remained as high as in the parental CS101B strain. The ability to utilize l-ornithine, l-arginine, putrescine, l-proline, and glycine as a nitrogen source was preserved in the mutants. The genetic lesions resulting in the loss of GABA transport, gabP5 and gabP9, mapped in the gab gene cluster in close linkage to gabT and gabD, the structural genes of GSST and SSDH, and to gabC, a gene controlling the utilization of GABA, arginine, putrescine, and ornithine. The synthesis of the GABA transport carrier is subject to dual physiological control by (i) catabolite repression and (ii) nitrogen availability. Experiments with glutamine synthetase (EC 6.3.1.2)-negative and with glutamine synthetase-constitutive strains strongly indicate that this enzyme is the effector in the regulation of GABA carrier synthesis by route (ii).

Regulation of glutamine synthetase formation in Escherichia coli: characterization of mutants lacking the uridylyltransferase

A lambda phage (lambdaNK55) carrying the translocatable element Tn10, conferring tetracycline resistance (Tetr), has been utilized to isolate glutamine auxotrophs of Escherichia coli K-12. Such strains lack uridylyltransferase as a result of an insertion of the TN10 element in the glnD gene. The glnD::Tn10 insertion has been mapped at min 4 on the E. coli chromosome and 98% contransducible by phage P1 with dapD. A lambda transducing phage carrying the glnD gene has been identified. A glnD::Tn10 strain synthesizes highly adenylylated glutamine synthetase under all conditions of growth and fails to accumulate high levels of glutamine synthetase in response to nitrogen limitation. However, this strain, under nitrogen-limiting conditions, allows synthesis of 10 to 20 milliunits of biosynthetically active glutamine synthetase per mg of protein, which is sufficient to allow slow growth in the absence of glutamine. The GlnD phenotype in E. coli can be suppressed by the presence of mutations which increase the quantity of biosynthetically active glutamine synthetase.

Glutamine synthetase of Klebsiella aerogenes: properties of glnD mutants lacking uridylyltransferase

The glnD mutation of Klebsiella aerogenes is cotransducible by phage P1 with pan (requirement for pantothenate) and leads to a loss of uridylytransferase and uridylyl-removing enzyme, components of the glutamine synthetase adenylylation system. This defect results in an inability to deadenylylate glutamine synthetase rapidly and in a requirement for glutamine for normal growth. Suppression of the glnD mutation are located at the glutamine synthetase structural gene glnA.

Catabolic N2-acetylornithine 5-aminotransferase of Klebsiella aerogenes: control of synthesis by induction, catabolite repression, and activation by glutamine synthetase

Klebsiella aerogenes formed two N2-acetylornithine 5-aminotransferases (ACOAT) which were separable by diethylaminoethyl-cellulose chromatography. One ACOAT was repressed when the cells grew on arginine-containing medium, indicating its function in arginine biosynthesis. The second ACOAT was induced when arginine or ornithine was present in the medium as the sole source of carbon or nitrogen, suggesting its function in the catabolism of these compounds. The induced enzyme was purified almost to homogeneity. Its molecular weight is 59,000; it is a pyridoxal 5-phosphate-dependent enzyme and exhibits activity with N2-acetylornithine (Km = 1.1 mM) as well as with ornithine (Km = 5.4 mM). ACOAT did not catalyze the transamination of putrescine or 4-aminobutyrate. The best amino acceptor was 2-ketoglutarate (Km = 0.7 mM). ACOAT formation was subject to catabolite repression exerted by glucose when ammonia was present in excess. When the cells were deprived of nitrogen, ACOAT escaped from catabolite repression. This activation was mediated by glutamine synthetase as shown by the fact that mutants affected in the regulation or synthesis of glutamine synthetase were also affected in the control of ACOAT formation.

Regulation of gamma-aminobutyric acid degradation in Escherichia coli by nitrogen metabolism enzymes

The possible role of glutamate dehydrogenase, glutamate synthase, and glutamine synthetase in the regulation of enzyme formation in the gamma-aminobutyric acid (GABA) catabolic pathway of Escherichia coli K-12 was investigated. Evidence is presented indicating that glutamine synthetase acts as a positive regulator in the E. coli GABA control system. Mutations impairing glutamate synthase activity prevent the depression of the enzymes of the GABA pathway in ammonia-limited glucose media. However, mutations resulting in constitutive synthesis of glutamine synthetase (GlnC) restore the ability of the glutamate synthase-less mutants to grow in glucose-GABA media and result in depressed synthesis of the GABA enzymes. It is suggested that the loss of glutamate synthesis activity affects the GABA control system indirectly by lowering glutamine synthetase levels.

gltB gene and regulation of nitrogen metabolism by glutamine synthetase in Escherichia coli

A mutant (gltB) of Escherichia coli lacking glutamate synthase (GOGAT) was unable to utilize a wide variety of compounds as sole nitrogen source (e.g., arginine, proline, gamma-aminobutyrate, and glycine). Among revertants of these Asm- strains selected on one of these compounds (e.g., arginine, proline, or gamma-aminobutyrate) were those that produce glutamine synthetase (GS) constitutively (GlnC phenotype). These revertants had a pleiotropically restored ability to grow on compounds that are metabolized to glutamate. This suggested that the expression of the genes responsible for the metabolism of these nitrogen sources was regulated by GS. An examination of the regulation of proline oxidase confirmed this hypothesis. The differential sensitivities of GlnC and wild-type strains to low concentrations (0.1 mM) of the glutamine analog L-methionine-DL-sulfoximine supported the conclusion that the synthesis of a glutamine permease was also positively controlled by GS. During the course of this study we found that the reported position of the locus (gltB) for glutamate synthase is incorrect. We have relocated this gene to be 44% linked to the argG locus by P1 transduction. Further mapping has shown that the locus previously called aspB is in reality the gltB locus and that the "suppressor" of the aspB mutation (A. M. Reiner, J. Bacteriol. 97:1431-1436, 1969) is the locus for glutamate dehydrogenase (gdhA).

Autogenous regulation of the synthesis of glutamine synthetase in Klebsiella aerogenes

We isolated an F' episome of Escherichia coli carrying the glnA+ gene from K. aerogenes and an F' episome of E. coli carrying the glnA4 allele from K. aerogenes responsible for the constitutive synthesis of glutamine synthetase. Complementation tests with these episomes showed that the glnA4 mutation (leading to the constitutive synthesis of active glutamine synthetase) was in the gene identified by mutations glnA20, glnA51, and glnA5 as the structural gene for glutamine synthetase. By using these merodiploid strains we were able to show that the glnA51 mutation lead to the synthesis of a glutamine synthetase that lacked enzymatic activity but fully retained its regulatory properties. Finally, we discuss a model that explains the several phenotypes associated with mutations such as glnA4 located within the structural gene for glutamine synthetase leading to constitutive synthesis of active glutamine synthetase.

Regulatory mutations in the Klebsiella aerogenes structural gene for glutamine synthetase

Glutamine synthetase could be repressed several hundredfold rather than 6- to 10-fold as previously reported. Ammonia was not the primary repression signal for glutamine synthetase. Repression appeared to be mediated by a high level of glutamine and probably by a high ratio of glutamine to alpha-ketoglutarate. Mutations in glnA (the structural gene for glutamine synthetase) were seen to fall into three phenotypic groups: glutamine auxotrophs that produced no detectable glnA product; glutamine auxotrophs that produced a glnA product lacking enzymatic activity (and hence repressibility by ammonia) but were repressible under appropriate conditions; and glutamine synthetase regulatory mutants, whose glnA product was enzymatically active and not repressible under any conditions.

Alteration of the Bacillus subtilis glutamine synthetase results in overproduction of the enzyme

A mutational leading to glutamine auxotrophy was located near a 5-fluorouracil resistance marker in the citB-thyA region of the Bacillus subtilis chromosome. This mutation resulted in a glutamine synthetase with altered kinetic and feedback properties. The specific activity of manganese-stimulated glutamine synthetase activity in crude extracts was 18-fold higher, and the magnesium-stimulated activity was about 30% that of the wild type. Quantitation of the enzyme by precipitation with antibody prepared against pure enzyme confirmed the presence of high enzyme levels in the mutant. This mutation is very closely linked (recombination index of 0.03) to another glutamine auxotroph containing enzyme with altered electrophoretic and heat sensitivity properties. Mutations in the structural gene for glutamine synthetase may result not only in altered catalytic and regulatory properties but also in altered production of the enzyme.

Urease of Klebsiella aerogenes: control of its synthesis by glutamine synthetase

Urease was purified 24-fold from extracts of Klebsiella aerogenes. The enzyme has a molecular weight of 230,000 as determined by gel filtration, is highly substrate specific, and has a Km for urea of 0.7 mM. A mutant strain lacking urease was isolated; it failed to grow with urea as the sole source of nitrogen but did grow on media containing other nitrogen sources such as ammonia, histidine, or arginine. Urease was present at a high level when the cells were starved for nitrogen; its synthesis was repressed when the external ammonia concentration was high. Formation of urease did not require induction by urea and was not subject to catabolite repression. Its synthesis was controlled by glutamine synthetase. Mutants lacking glutamine synthetase failed to produce urease, and mutants forming glutamine synthetase at a high constitutive level also formed urease constitutively. Thus, the formation of urease is regulated like that of other enzymes of K. aerogenes capable of supplying the cell with ammonia or glutamate.

Characterization of Salmonella typhimurium mutants with altered glutamine synthetase activity

A number of glutamine auxotrophs of Salmonella typhimurium were isolated and characterized genetically. Three of the mutations appear to be closely linked and are complemented by episomes carrying the glnA region of Escherichia coli. The lesions in these strains are approximately 20% linked by P1 transduction with a mutation in the rha gene, but are unlinked to ilv. Another mutation causing glutamine auxotrophy in strain JB674 is genetically distinct from the others. Strain JB674 grown in glucose medium containing ammonia as the nitrogen source has reduced levels of glutamine synthetase that is more adenylylated than in the parent strain, suggesting that the enzyme can not be deadenylylated normally. The lesion causing glutamine auxotrophy in JB674 lies in the region corresponding to the glnB and glnE genes affecting glutamine synthetase modification in Klebsiella areogenes. Four Gln+ revertants of JB674 have glutamine synthetase activities 4 to 6 fold higher than normal. One mutation causing this increased enzyme synthesis has been shown by three-factor crosses with the glnA mutations to lie near or within the glnA gene.

Regulation of enzyme synthesis by the glutamine synthetase of Salmonella typhimurium: a factor in addition to glutamine synthetase is required for activation of enzyme formation

In Klebsiella aerogenes but not in Salmonella typhimurium glutamine synthetase can function during nitrogen-limited growth to increase the rate of synthesis of histidase from the hut genes of S. typhimurium 15-59 (hutS. 15-59). Formation of proline oxidase is also not increased in nitrogen-limited cultures of S. typhimurium. However, in hybrid strains of Escherichia coli or K. aerogenes, the glutamine synthetase of S. typhimurium activates synthesis of histidase from the hutS. 15-59 genes. Apparently, glutamine synthetase is necessary but not sufficient for activation of transcription of the hut genes; another factor must also be present. This factor is active in both K. aerogenes and E. coli but is missing or altered in S. typhimurium.

Regulation of PRPP and nucleoside tri and tetraphosphate pools in Escherichia coli under conditions of nitrogen starvation

The ribonucleoside triphosphate, deoxyribonucleoside triphosphate, 3' -diphosphate guanosine 5' -diphosphate (ppGpp), and 5-phosphoribosyl 1-pyrophosphate (PRPP) pools in Escherichia coli B were determined by thin-layer chromatography during changing conditions to ammonium starvation. The intracellular concentrations of all nucleotides were found to change in a well-defined order several minutes before andy observed change in the optical density of the culture. The levels of purine nucleoside triphosphates (adenosine 5' -triphosphate [CTP], dCTP) and uridine nucleotides (uridine 5' -triphosphate, deoxythymidine 5'-triphosphate). The deoxyribonucleotides thus behaved as the ribonucleotides. The levels of ppGpp increased 11-fold after the decrease in uridine nucleotides, when the accumulation of stable ribonucleic acid (RNA) stopped. The level of the nucleotide pool did not stabilize until 30 min after the change in optical density. The pool of dGTP dropped concomitantly with the pool of CTP. The nucleotide precursor PRPP exhibited a transient increase, wtih maximum value of four times the exponential levels at the onset of starvation. Apparently the cell adjusts early to starvation by reducing either the phosphorylating activity or the nucleotide biosynthetic activity. As in other downshift systems, the accumulation of stable RNA stopped before the break in optical density and before the stop in protein accumulation. Cell divisions were quite insensitive to the control mechanisms operating on RNA and protein accumulation under ammonium starvation, since the cells continued to divide for 21 min without any net accumulation of RNA.

Transcription of the hut operons of Salmonella typhimurium

We have measured, by ribonucleic acid-deoxyribonucleic acid hybrid formation, the amounts of hut-specific ribonucleic acid contained in extracts of various mutant strains of Salmonella typhimurium. Our data are consistent with a model in which regulation of Hut enzyme production occurs at the level of transcription and support earlier genetic evidence indicating that all of the hut genes are transcribed in the clockwise direction on the S. typhimurium chromosome. These results also suggest that promoter sites of the two hut operons may differ in their ability to initiate transcription.

Glutamine synthetase of Klebsiella aerogenes: genetic and physiological properties of mutants in the adenylylation system

Mutations resulting in defects in the adenylylation system of glutamine synthetase (GS) affect the expression of glnA, the structural gene for GS. Mutants with lesions in glnB are glutamine auxotrophs and contain repressed levels of highly adenylylated GS. Glutamine-independent revertants of the glnB3 mutant have acquired an additional mutation at the glnE site. The glnE54 mutant is incapable of adenylylating GS and produces high levels of enzyme, even when ammonia is present in the growth medium. The fact that mutations in glnB and glnE simultaneously disturb both the normal adenylylation and repression patterns of GS in Klebsiella aerogenes indicates that the adenylylation system, or adenylylation state, of GS is critical for the regulation of synthesis of GS.

Regulation of glnA messinger ribonucleic acid synthesis in Klebsiella aerogenes

We examined wild-type and mutant strains of Klebsiella aerogenes for the relative amounts of ribonucleic acid (RNA) hybridizing specifically to deoxyribonucleic acid from a transducing phage carrying glnAK, the structural gene for glutamine synthetase. Our data showed a positive correlation between the intracellular level of glutamine synthetase and the level of glnA messenger RNA; we were unable to detect glnA messinger RNA in strains devoid of glutamine synthetase protein. Therefore, it is possible that transcription of glnA is not regulated simply by repression mediated through the glutamine synthetase protein; rather, autogenous control in this system may involve activation of transcription. Our experiments also suggest that the promotor of the glnA gene is located at the rha proximal end of the gene.

Biochemical parameters of glutamine synthetase from Klebsiella aerogenes

The glutamine synthetase (GS) from Klebsiella aerogenes is similar to that from Escherichia coli in several respects: (i) it is repressed by high levels of ammonia in the growth medium; (ii) its biosynthetic activity is greatly reduced by adenylylation; and (iii) adenylylation lowers the pH optimum and alters the response of the enzymes to various inhibitors in the gamma-glutamyl transferase (gammaGT) assay. There are, however, several important differences: (i) the isoactivity point for the adenylylated and non-adenylylated forms in the gammaGT assay occurs at pH 7.55 in K. aerogenes and at pH 7.15 in E. coli; (ii) the non-adenylylated form of the GS from K. aerogenes is stimulated by 60 mM MgCl2 in the gammaGT assay at pH 7.15. A biosynthetic reaction assay that correlates well with number of non-adenylylated enzyme subunits, as determined by the method of Mg2+ inhibition of the gammaGT assay, is described. Finally, we have found that it is necessary to use special methods to harvest growing cells to prevent changes in the adenylylation state of GS from occurring during harvesting.

Pleiotropic mutants of Aspergillus nidulans altered in carbon metabolism

Mutants altered in carbon catabolite regulation have been isolated by selecting for mutants of the areA217 strain capable of using acetamide as the sole nitrogen source in the presence of sucrose. In addition to creA mutants described previously be Arst and Cove, strains with mutations in two new genes, creB and cre C, have been found. The creB and creC mutants grow poorly on some sole carbon sources and have low levels of some enzymes of carbon catabolism e.g. beta-galactosidase and D-quinate dehydrogenase. The creB and creC mutants are hypersensitive to fluoroacetate, fluoroacetamide and allyl alcohol in the presence of glucose or sucrose but not glycerol; and the enzymes, acetamidase and alcohol dehydrogenase, are less sensitive to carbon catabolite repression than the wild-type strain. Extracellular protease and alpha-glucosidase enzyme activities are elevated in creB and creC mutants, while L-proline and L-glutamate uptake capacities are lower in both the presence and absence of glucose. Interactions between creA, B and C mutations have been investigated in double mutants, and the dominance properties of creB and creC mutants determined. The results indicate that the creB and creC genes may have a regulatory role in the control of carbon catabolism.