RESUMEN

L-lysine and other amino acids are commonly produced through fermentation using strains of heterotrophic bacteria such as Corynebacterium glutamicum. Given the large amount of sugar this process consumes, direct photosynthetic production is intriguing alternative. In this study, we report the development of a cyanobacterium, Synechococcus sp. strain PCC 7002, capable of producing L-lysine with CO2 as the sole carbon-source. We found that heterologous expression of a lysine transporter was required to excrete lysine and avoid intracellular accumulation that correlated with poor fitness. Simultaneous expression of a feedback inhibition resistant aspartate kinase and lysine transporter were sufficient for high productivities, but this was also met with a decreased chlorophyll content and reduced growth rates. Increasing the reductant supply by using NH4+, a more reduced nitrogen source relative to NO3-, resulted in a two-fold increase in productivity directing 18% of fixed carbon to lysine. Given this advantage, we demonstrated lysine production from media formulated with a municipal wastewater treatment sidestream as a nutrient source for increased economic and environmental sustainability. Based on our results, we project that Synechococcus sp. strain PCC 7002 could produce lysine at areal productivities approaching that of sugar cane to lysine via fermentation using non-agricultural lands and low-cost feedstocks.

Asunto(s)

Sistemas de Transporte de Aminoácidos , Aspartato Quinasa , Proteínas Bacterianas , Corynebacterium glutamicum/genética , Fotosíntesis , Synechococcus , Sistemas de Transporte de Aminoácidos/biosíntesis , Sistemas de Transporte de Aminoácidos/genética , Aspartato Quinasa/biosíntesis , Aspartato Quinasa/genética , Proteínas Bacterianas/biosíntesis , Proteínas Bacterianas/genética , Corynebacterium glutamicum/metabolismo , Lisina , Synechococcus/genética , Synechococcus/metabolismo

RESUMEN

The ever-changing environment of a bacterial cell requires sophisticated mechanisms to adjust gene expression in response to changes in nutrient availability. L box riboswitch RNAs regulate gene expression in response to cellular lysine (lys) concentrations in the absence of additional regulatory factors. In Bacillus subtilis, binding of lysine (lys) to the L box RNA causes premature transcription termination in the leader region upstream of the lysC coding sequence. To date, little is known about the specific RNA-lys interactions required for transcription termination. In this study, we characterize features of the B. subtilis lysC leader RNA responsible for lys specificity, and structural elements of the lys molecule required for recognition. The wild-type lysC leader RNA can recognize and discriminate between lys and lys analogs. We identified leader RNA variants with mutations in the lys-binding pocket that exhibit changes in the specificity of ligand recognition. These data demonstrate that lysC leader RNA specificity is the result of recognition of ligand features through a series of distinct interactions between lys and nucleotides that comprise the lys-binding pocket, and provide insight into the molecular mechanisms employed by L box riboswitch RNAs to bind and recognize lys.

Asunto(s)

Bacillus subtilis/genética , Lisina/farmacología , ARN Bacteriano/química , Riboswitch , Regiones no Traducidas 5' , Aspartato Quinasa/biosíntesis , Aspartato Quinasa/genética , Bacillus subtilis/enzimología , Secuencia de Bases , Sitios de Unión , Regulación Bacteriana de la Expresión Génica , Ligandos , Lisina/análogos & derivados , Lisina/química , Datos de Secuencia Molecular , Mutación , Potasio/química , Transcripción Genética

RESUMEN

Initial steps of aspartate-derived biosynthesis pathway (Asp pathway) producing Lys, Thr, Met and Ile are catalyzed by bifunctional (AK/HSD) and monofunctional (AK-lys) aspartate kinase (AK) enzymes. Here, we show that transcription of all AK genes is negatively regulated under darkness and low sugar conditions. By using yeast one-hybrid assays and complementary chromatin immunoprecipitation analyses in Arabidopsis cells, the bZIP transcription factors ABI5 and DPBF4 were identified, capable of interacting with the G-box-containing enhancer of AK/HSD1 promoter. Elevated transcript levels of DPBF4 and ABI5 under darkness and low sugar conditions coincide with the repression of AK gene expression. Overexpression of ABI5, but not DPBF4, further increases this AK transcription suppression. Concomitantly, it also increases the expression of asparagines synthetase 1 (ASN1) that shifts aspartate utilization towards asparagine formation. However, in abi5 or dpbf4 mutant and abi5, dpbf4 double mutant the repression of AK expression is maintained, indicating a functional redundancy with other bZIP-TFs. A dominant-negative version of DPBF4 fused to the SRDX repressor domain of SUPERMAN could counteract the repression and stimulate AK expression under low sugar and darkness in planta. This effect was verified by showing that DPBF4-SRDX fails to recognize the AK/HSD1 enhancer sequence in yeast one-hybrid assays, but increases heterodimmer formation with DPBF4 and ABI5, as estimated by yeast two-hybrid assays. Hence it is likely that heterodimerization with DPBF4-SRDX inhibits the binding of redundantly functioning bZIP-TFs to the promoters of AK genes and thereby releases the repressing effect. These data highlight a novel transcription control of the chloroplast aspartate pathway that operates under energy limiting conditions.

Asunto(s)

Proteínas de Arabidopsis/biosíntesis , Arabidopsis/enzimología , Arabidopsis/genética , Aspartato Quinasa/biosíntesis , Factores de Transcripción con Cremalleras de Leucina de Carácter Básico/metabolismo , Oscuridad , Sacarosa/metabolismo , Secuencia de Aminoácidos , Arabidopsis/metabolismo , Proteínas de Arabidopsis/genética , Proteínas de Arabidopsis/metabolismo , Aspartato Quinasa/genética , Aspartato Quinasa/metabolismo , Secuencia de Bases , Factores de Transcripción con Cremalleras de Leucina de Carácter Básico/genética , Regulación de la Expresión Génica de las Plantas , Genes de Plantas , Variación Genética , Datos de Secuencia Molecular , Mutación , Regiones Promotoras Genéticas , Secuencias Reguladoras de Ácidos Nucleicos , Activación Transcripcional

RESUMEN

The first two genes of the threonine pathway, ask and asd, were cloned and sequenced from the aminoethoxyvinylglycine-producing Streptomyces sp. NRRL 5331. The two genes are organized in a bicistronic operon. ask, encoding the apartokinase (ASK), is located upstream from asd. The presence of a ribosome-binding site within the ask sequence suggests that this open reading frame encodes two overlapping proteins. The formation of both subunits of the aspartokinase from a single gene was studied using antibodies raised against the C-terminal end of the aspartokinase subunits. Disruption of asd results in a significant decrease of aminoethoxyvinylglycine production, thus supporting the involvement of the ask-asd operon in the biosynthesis of this metabolite. This is the first report in which a gene cluster for the first two steps of aminoethoxyvinylglycine biosynthesis is characterized.

Asunto(s)

Aspartato Quinasa/genética , Aspartato-Semialdehído Deshidrogenasa/genética , Glicina/análogos & derivados , Glicina/biosíntesis , Glicina/genética , Operón , Streptomyces/genética , Secuencias de Aminoácidos , Secuencia de Aminoácidos , Aspartato Quinasa/biosíntesis , Aspartato-Semialdehído Deshidrogenasa/biosíntesis , Proteínas Bacterianas/genética , Secuencia de Bases , Clonación Molecular , Codón Iniciador , Codón de Terminación , ADN Bacteriano/química , ADN Bacteriano/aislamiento & purificación , Eliminación de Gen , Expresión Génica , Orden Génico , Genes Bacterianos , Genes Sobrepuestos , Glicina/análisis , Datos de Secuencia Molecular , ARN Mensajero/análisis , Análisis de Secuencia de ADN , Homología de Secuencia , Transcripción Genética

RESUMEN

In Escherichia coli and Bacillus subtilis, long leader sequences are found upstream of the lysC coding sequences which encode lysine-sensitive aspartokinase. Highly conserved regions exist between these sequences. Mutations leading to constitutive expression of the E. coli lysC gene have been localised within these conserved regions, indicating that they participate in the lysine-mediated repression mechanism of lysC expression.

Asunto(s)

Aspartato Quinasa/genética , Escherichia coli/genética , Secuencias Reguladoras de Ácidos Nucleicos , Aspartato Quinasa/biosíntesis , Secuencia de Bases , Escherichia coli/enzimología , Regulación Bacteriana de la Expresión Génica , Genes Bacterianos , Datos de Secuencia Molecular , Homología de Secuencia de Ácido Nucleico

RESUMEN

The nucleotide sequence of a 1.1 kb XhoI-HindIII fragment downstream of the malate dehydrogenase (mdh) gene of Thermus flavus revealed the presence of an ORF and an incomplete ORF lacking its NH2-terminal portion, in the opposite orientation to that of the mdh gene. These two genes overlapped with each other, sharing two base pairs, suggesting that these genes are co-transcribed in a single mRNA. One ORF (termed gpt) encoded a protein of 154 amino acids showing significant amino acid sequence similarity to purine phosphoribosyltransferases, such as xanthine-guanine phosphoribosyltransferase of Escherichia coli and human hypoxanthine phosphoribosyltransferase. Cloning and sequencing of the upstream region of the gpt gene, together with sequence comparison of the gene product encoded by the region upstream of gpt, suggested that the upstream ORF encoded two in-frame overlapping aspartokinase genes, askA, encoding the alpha-subunit of 405 amino acids, and askB, encoding the beta-subunit of 161 amino acids, which was part of the 3' portion of askA. Consistent with the sequence data, the askAB and the gpt genes conferred the heat-stable enzyme activities of aspartokinase and phosphoribosyltransferase, respectively, on E. coli. Preliminary characterization of these enzymes produced in E. coli is described.

Asunto(s)

Aspartato Quinasa/genética , Operón , Pentosiltransferasa/genética , Thermus/enzimología , Thermus/genética , Secuencia de Aminoácidos , Aspartato Quinasa/biosíntesis , Aspartato Quinasa/metabolismo , Secuencia de Bases , Clonación Molecular , Cartilla de ADN , Escherichia coli , Expresión Génica , Cinética , Datos de Secuencia Molecular , Sistemas de Lectura Abierta , Pentosiltransferasa/biosíntesis , Pentosiltransferasa/metabolismo , Reacción en Cadena de la Polimerasa , Proteínas Recombinantes/biosíntesis , Proteínas Recombinantes/metabolismo , Homología de Secuencia de Aminoácido , Homología de Secuencia de Ácido Nucleico , Especificidad por Sustrato

Asunto(s)

Aspartato Quinasa/metabolismo , Hidroliasas/metabolismo , Lisina/metabolismo , Plantas Modificadas Genéticamente/metabolismo , Treonina/metabolismo , Aspartato Quinasa/biosíntesis , Biotecnología/métodos , Escherichia coli/enzimología , Escherichia coli/genética , Expresión Génica , Hidroliasas/biosíntesis , Cinética , Hojas de la Planta , Proteínas de Plantas/biosíntesis , Proteínas Recombinantes/metabolismo

RESUMEN

We have cloned the yeast allele HOM3-R2, that codes for a mutant aspartate kinase which is insensitive to feedback inhibition by threonine, by gap-repair. A strain carrying this allele in a multicopy plasmid, or integrated into the genome, accumulates 14-times and 8-times more threonine than the wild-type, respectively. The sequence of the mutant allele differs from that of the wild-type in a single base pair change, namely a G by an A, at position 1355 in the open reading frame. The fact that the presence of this mutant allele in a cell induces threonine overproduction points to aspartate kinase as the key enzyme in the regulation of threonine biosynthesis in yeast.

Asunto(s)

Alelos , Aspartato Quinasa/genética , Genes Fúngicos , Saccharomyces cerevisiae/genética , Saccharomyces cerevisiae/metabolismo , Treonina/biosíntesis , Aspartato Quinasa/biosíntesis , Clonación Molecular , Genotipo , Sistemas de Lectura Abierta , Mutación Puntual , Mapeo Restrictivo

RESUMEN

Regulation of aspartate kinase and diaminopimelate decarboxylase activities in Streptococcus bovis and Enterococcus faecium cell-free extracts was studied. The levels of synthesis of aspartate kinase and diaminopimelate decarboxylase in both microorganisms are growth-dependent. The synthesis of these enzymes is depressed by lysine, but the activity of aspartate kinase is induced by addition of this amino acid and threonine to the reaction system. Meso-diaminopimelate dehydrogenase activity was not found in the extracts of Streptococcus bovis and Enterococcus faecium. The data excludes the possibility of lysine formation via six enzyme reactions.

Asunto(s)

Aspartato Quinasa/metabolismo , Proteínas Bacterianas , Carboxiliasas/metabolismo , Enterococcus faecium/enzimología , Lisina/biosíntesis , Streptococcus bovis/enzimología , Aspartato Quinasa/antagonistas & inhibidores , Aspartato Quinasa/biosíntesis , Carboxiliasas/antagonistas & inhibidores , Carboxiliasas/biosíntesis , Catálisis , Sistema Libre de Células , Enterococcus faecium/crecimiento & desarrollo , Enterococcus faecium/metabolismo , Streptococcus bovis/crecimiento & desarrollo , Streptococcus bovis/metabolismo

RESUMEN

Two promoters required for expression of the ask-asd genes, encoding aspartokinase (AK) and aspartate-semialdehyde dehydrogenase (ASD), in Corynebacterium flavum N13, askP1 and askP2, have been identified by deletion analysis and S1 nuclease mapping. Transcription from askP1 initiates 35 and 38 bp upstream of the ask structural gene. A second promoter, askP2, lies within the ask coding region, upstream of the translation start site of the AK beta subunit and can direct the expression of AK beta and ASD. Western immunoblot analysis and heterologous expression in Escherichia coli demonstrate that two separate polypeptides, a 44.8-kDa alpha subunit and an 18.5-kDa beta subunit, are expressed from the C. flavum N13 ask gene from distinct, in-frame translation initiation sites. A second AK mutation, G345D, which reduces the sensitivity of AK to concerted feedback inhibition by threonine plus lysine, was identified.

Asunto(s)

Aspartato Quinasa/genética , Aspartato-Semialdehído Deshidrogenasa/genética , Corynebacterium/genética , Genes Bacterianos/genética , Operón/genética , Secuencia de Aminoácidos , Aspartato Quinasa/biosíntesis , Secuencia de Bases , Corynebacterium/enzimología , Escherichia coli/genética , Datos de Secuencia Molecular , Sistemas de Lectura Abierta/genética , Regiones Promotoras Genéticas/genética , Biosíntesis de Proteínas , ARN Mensajero/genética , Proteínas Recombinantes/biosíntesis , Mapeo Restrictivo , Transcripción Genética

RESUMEN

Aspartokinase II from Bacillus subtilis was shown by immunochemical methods to be regulated by degradation in response to starvation of cells for various nutrients. Ammonium starvation induced the fastest aspartokinase II decline (t1/2 = 65 min), followed by amino acid starvation (t1/2 = 80 min) and glucose limitation (t1/2 = 120 min). Loss of enzyme activity was closely correlated with the disappearance of the alpha subunit; degradation of the beta subunit was somewhat delayed or slower under some conditions. Pulse-chase experiments demonstrated that aspartokinase II was stable during exponential growth; the synthesis of the enzyme rapidly declined in response to nutrient exhaustion. The degradation of aspartokinase II was interrupted by inhibitors of energy production and protein synthesis but was not changed in a mutant lacking a major intracellular protease. Mutants lacking a normal stringent response displayed only a slight decrease in the rate of aspartokinase II degradation, even though aspartate transcarbamylase was degraded more slowly in the same mutant cells. These results indicate that although energy-dependent degradation of biosynthetic enzymes is a general phenomenon in nutrient-starved B. subtilis cells, the degradation of specific enzymes probably involves different pathways.

Asunto(s)

Aspartato Quinasa/metabolismo , Bacillus subtilis/enzimología , Isoenzimas/metabolismo , Fosfotransferasas/metabolismo , Secuencia de Aminoácidos , Amoníaco/farmacología , Aspartato Quinasa/biosíntesis , Aspartato Quinasa/genética , Bacillus subtilis/efectos de los fármacos , Bacillus subtilis/crecimiento & desarrollo , Cloranfenicol/farmacología , Glucosa/metabolismo , Gliceraldehído-3-Fosfato Deshidrogenasas/genética , Isoenzimas/biosíntesis , Cinética , Datos de Secuencia Molecular , Homología de Secuencia de Ácido Nucleico

RESUMEN

The extents of thialysine and selenalysine incorporation into cell proteins were compared in E. coli KL16 and in a mutant able to grow equally well in the presence or in the absence of both lysine analogs. The mutant differs from the parental strain in the repression of aspartokinase III (AKIII), the first enzyme of the lysine biosynthetic pathway. No analog incorporation into proteins was observed in mutant cells grown in the presence of either analog, whereas a marked analog incorporation was observed in the parental strain, where up to 17% and 12% of protein lysine can be substituted by thialysine and selenalysine respectively. In the parental strain grown in media containing either analog at different concentration the extent of analog incorporation into proteins is related to the extent of AKIII repression.

Asunto(s)

Aspartato Quinasa/biosíntesis , Escherichia coli/metabolismo , Lisina/análogos & derivados , Lisina/metabolismo , Compuestos de Organoselenio , Biosíntesis de Proteínas , Aspartato Quinasa/genética , Cisteína/análogos & derivados , Cisteína/metabolismo , Represión Enzimática , Escherichia coli/genética , Isoenzimas , Mutación , Selenio/metabolismo

RESUMEN

A thialysine-resistant mutant of E. coli strain KL16 also shows a lower sensitivity to selenalysine, the lysine analog containing selenium. No difference between the mutant and the parental strain has been shown regarding the affinities of the transport systems and the lysyl-tRNA synthetase for selenalysine, thialysine and lysine as well as the inhibitory effects of these three aminoacids on the activity of the lysine biosynthetic pathway. A marked difference between the two strains has been evidenced in the AK III repression: in the mutant the repression by selenalysine, thialysine and lysine is much lower than in the parental strain.

Asunto(s)

Cisteína/análogos & derivados , Escherichia coli/genética , Lisina/análogos & derivados , Compuestos de Organoselenio , Selenio/farmacología , Aspartato Quinasa/biosíntesis , Cisteína/farmacología , Farmacorresistencia Microbiana , Represión Enzimática , Escherichia coli/efectos de los fármacos , Escherichia coli/enzimología , Cinética , Lisina/farmacología , Lisina-ARNt Ligasa/metabolismo , Mutación

RESUMEN

The effect of the cephalosporin precursors and amino acids of the aspartic acid family on antibiotic production by Streptomyces clavuligerus was investigated DL-meso-Diaminopimelate and L-lysine each stimulated specific antibiotic production by 75%. A fourfold increase in specific production was obtained by simultaneous addition of the two compounds. The stimulation could be further increased by adding valine to the two effectors. In the streptomycetes the alpha-aminoadipyl side chain of the cephalosporin antibiotics is derived from lysine. Streptomycetes, like other bacteria, are expected to produce lysine from aspartic acid; therefore, the feedback control mechanisms operating in the aspartic acid family pathway of S. clavuligerus, which may affect the flow of carbon to alpha-aminoadipic acid, were investigated. Threonine inhibited antibiotic production by 41% when added to minimal medium at a concentration of 10 mM. Simultaneous addition of 10 mM lysine completely reversed this inhibition. The aspartokinase of S. clavuligerus was found to be subject to concerted feedback inhibition by threonine and lysine. Threonine may act to limit the supply of lysine available for cephamycin C biosynthesis via this concerted mechanism. Single or simultaneous addition of any other amino acid of the aspartate family in the in vitro assay did not inhibit aspartokinase activity. Activity was stimulated by lysine. Aspartokinase biosynthesis was partially repressed by methionine or isoleucine at concentrations higher than 10 mM. Methionine, but not isoleucine, inhibited cephamycin C synthesis by 27% when added to minimal medium at a concentration of 10 mM. Dihydrodipicolinate synthetase, the first specific enzyme of the lysine branch, was not inhibited by lysine but was partially inhibited by high concentrations of 2,6-diaminopimelate and alpha-aminoadipate; it was slightly repressed by diaminopimelic acid. Homoserine dehydrogenase activity was inhibited by threonine and partially repressed by isoleucine. It appears that S. clavuligerus aspartokinase is a key step in the control of carbon flow toward alpha-aminoadipic acid.

Asunto(s)

Oxidorreductasas de Alcohol/análisis , Aminoácidos/farmacología , Aspartato Quinasa/análisis , Cefalosporinas/biosíntesis , Cefamicinas/biosíntesis , Homoserina Deshidrogenasa/análisis , Hidroliasas/análisis , Fosfotransferasas/análisis , Streptomyces/metabolismo , Ácido 2-Aminoadípico/metabolismo , Aspartato Quinasa/biosíntesis , Homoserina Deshidrogenasa/biosíntesis , Hidroliasas/biosíntesis

RESUMEN

Mutants containing fusions of the lac gene to the lysC gene were isolated. In these, the expression of beta-galactosidase was regulated by lysine (and arginine), as previously described for aspartokinase III.

Asunto(s)

Aspartato Quinasa/biosíntesis , Escherichia coli/enzimología , Genes , Fosfotransferasas/biosíntesis , Aspartato Quinasa/genética , Represión Enzimática , Escherichia coli/genética , Lisina/farmacología , Mutación , Operón , Recombinación Genética , beta-Galactosidasa/biosíntesis

RESUMEN

Reduction in the amounts of activity of the first enzyme, aspartokinase (EC 2.7.2.4) and two branch-point enzymes, dihydrodipicolinic acid synthase (EC 4.2.1.52) and homoserine dehydrogenase (EC 1.1.1.3), located in the pathway for the synthesis of aspartate-family amino acids, occurred when cell suspension cultures of Daucus carota L. var. Danvers were grown in media containing 2 mM threonine or 2 mM lysine, endproducts of the pathway. Activity of the lysine-sensitive form of aspartokinase was decreased when cells were grown in medium containing lysine and the activity of the threonine-sensitive form was decreased when cells were grown in medium containing threonine. Activity of the branch-point enzyme leading to threonine synthesis, homoserine dehydrogenase, was decreased up to 70% in specific activity (units/mg protein) and relative activity (units/g fresh weight) when cells were grown in media containing lysine or threonine. Threonine had no effect on the relative activity of dihydrodipicolinic acid synthase, but decreased its specific activity. Lysine decreased the relative activity of the synthase by up to 40%, but had little effect on its specific activity. The decreased activities of the enzymes were apparently not due to binding of the inhibitory amino acids to the enzymes since homogenization of cells in buffer with 2 mM lysine and threonine did not decrease the measurable enzyme activities. These and other results presented suggest that both forms of the aspartokinase activity and homoserine dehydrogenase activity can be altered by supplementing the growth medium with lysine or threonine.

Asunto(s)

Oxidorreductasas de Alcohol/biosíntesis , Aspartato Quinasa/biosíntesis , Carboxiliasas/biosíntesis , Homoserina Deshidrogenasa/biosíntesis , Lisina/metabolismo , Fosfotransferasas/biosíntesis , Plantas/enzimología , Treonina/metabolismo , Aminoácidos/metabolismo , Células Cultivadas , Cinética , Plantas/metabolismo , Salicilatos/biosíntesis

Asunto(s)

Aspartato Quinasa/genética , Bacillus subtilis/genética , Genes Reguladores , Hidroliasas/genética , Fosfotransferasas/genética , Esporas Bacterianas/crecimiento & desarrollo , Aspartato Quinasa/biosíntesis , Bacillus subtilis/enzimología , Genes , Hidroliasas/biosíntesis , Biosíntesis de Proteínas , Factores de Tiempo

RESUMEN

A comparison was made of the repressibility of certain enzymes in the tyrosine, methionine, and lysine biosynthetic pathways in wild-type Salmonella typhimurium and a hisT mutant. The results show that (i) tyrosine represses the synthesis of the tyrosine-sensitive 3-deoxy-D-arabino-heptulsonic acid 7-phosphate synthetase and the tyrosine aminotransferase to the same extent in a hisT mutant as in wild type and (ii) there is no detectable alteration in the extent to which methionine represses O-succinylhomoserine synthetase or in the extent to which lysine represses the lysine-sensitive beta-aspartokinase as a result of the hisT mutation.

Asunto(s)

Lisina/biosíntesis , Metionina/biosíntesis , Mutación , Salmonella typhimurium/metabolismo , Tirosina/biosíntesis , 2-Isopropilmalato Sintasa/biosíntesis , 3-Desoxi-7-Fosfoheptulonato Sintasa/biosíntesis , Acetiltransferasas/biosíntesis , Aspartato Quinasa/biosíntesis , Represión Enzimática , Histidinol-Fosfatasa/biosíntesis , Lisina/farmacología , Metionina/farmacología , Salmonella typhimurium/enzimología , Tirosina/farmacología , Tirosina Transaminasa/biosíntesis

RESUMEN

A general survey of the regulation in lysine biosynthesis in Escherichia coli K12 is presented. No polygenic operon exists for the genes that code for enzymes of the lysine biosynthetic pathway. Lysyl-tRNA is not directly involved as a co-repressor in the pathway. Different regulation mechanisms must exist for the different enzymes. In the case of the last enzyme, diaminopimelate decarboxylase, its synthesis is induced in vivo by the lysine-sensitive aspartokinase under its non-inhibited allosteric conformation.

Asunto(s)

Escherichia coli/metabolismo , Genes Reguladores , Lisina/biosíntesis , Adenosina Trifosfato/metabolismo , Aspartato Quinasa/biosíntesis , Aspartato-Semialdehído Deshidrogenasa/biosíntesis , Carboxiliasas/biosíntesis , Represión Enzimática , Retroalimentación , Hidroliasas/biosíntesis , Isoenzimas/biosíntesis , Lisina-ARNt Ligasa/biosíntesis , Mutación , ARN Bacteriano/metabolismo , ARN de Transferencia/metabolismo , Transcripción Genética

RESUMEN

A method for isolating regulatory mutants for the synthesis of lysine biosynthetic enzymes in Escherichia coli is described. One of them is identified as a cis-dominant constitutive mutant for the synthesis of the lysine-sensitive asportokinase AK III (lysC gene).

Asunto(s)

Aspartato Quinasa/biosíntesis , Escherichia coli/enzimología , Genes Dominantes , Lisina/biosíntesis , Fosfotransferasas/biosíntesis , Alelos , Arginina/metabolismo , Aspartato Quinasa/metabolismo , Aspartato-Semialdehído Deshidrogenasa/biosíntesis , Técnicas Bacteriológicas , Mapeo Cromosómico , Colifagos , Conjugación Genética , Relación Dosis-Respuesta a Droga , Represión Enzimática , Escherichia coli/crecimiento & desarrollo , Escherichia coli/aislamiento & purificación , Factor F , Lisina/metabolismo , Mutación , Especificidad de la Especie , Transducción Genética