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Query: UNIPROT:P06889 (Mol)
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We asked if UGA suppression by charged tRNATrp, a process called UGA readthrough, is involved in the mechanism of attenuation of the tryptophan (trp) operon in Escherichia coli. For this purpose we used two mutations: strA(LD1) which causes restriction of UGA readthrough, and revA which partially overcomes the restriction of UGA readthrough caused by strA(LD1)(Engelberg-Kulka et al. 1982). trp attenuation was monitored by the regulation of the synthesis of the trp operon enzyme anthranilate synthetase (ASase) in trpR strains. We showed that the strA(LD1) mutation causes a significant increase in the level of synthesis of ASase in the presence of an excess of tryptophan, while the revA mutation reverses this effect, indicating that transcription termination at the trp attenuator site is relieved by restriction of UGA readthrough. Based on our results and the sequence data of the trp leader RNA of E. coli (Oxender et al. 1979), we offer a model for the involvement of the UGA readthrough process in trp attenuation. We suggest that the UGA readthrough process permits trp attenuation to respond to slight changes in the cellular concentration of charged tRNATrp.
Mol Gen Genet 1982
PMID:Studies on the involvement of the UGA readthrough process in the mechanism of attenuation of the tryptophan operon of Escherichia coli. 675 72

Twelve tryptophan auxotrophs of Rhizobium leguminosarum were characterized biochemically. They were grown in complex and minimal media with several carbon sources, in both limiting and excess tryptophan. Missing enzyme activities allowed assignment of all mutant to the trpE, trpD, trpB, or trpA gene, confirming earlier results with the same mutants (Johnston et al., Mol. Gen. Genet. 165:323-330, 1978). In regulatory experiments, only the first enzyme of the pathway, anthranilate synthase, responded (about 15-fold) to tryptophan excess or limitation.
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PMID:Regulation of tryptophan genes in Rhizobium leguminosarum. 706 83

Salicylate is a precursor of pyochelin in Pseudomonas aeruginosa and both compounds display siderophore activity. To elucidate the salicylate biosynthetic pathway, we have cloned and sequenced a chromosomal region of P. aeruginosa PAO1 containing two adjacent genes, designated pchB and pchA, which are necessary for salicylate formation. The pchA gene encodes a protein of 52 kDa with extensive similarity to the chorismate-utilizing enzymes isochorismate synthase, anthranilate synthase (component I) and p-aminobenzoate synthase (component I), whereas the 11 kDa protein encoded by pchB does not show significant similarity with other proteins. The pchB stop codon overlaps the presumed pchA start codon. Expression of the pchA gene in P. aeruginosa appears to depend on the transcription and translation of the upstream pchB gene. The pchBA genes are the first salicylate biosynthetic genes to be reported. Salicylate formation was demonstrated in an Escherichia coli entC mutant lacking isochorismate synthase when this strain expressed both the pchBA genes, but not when it expressed pchB alone. By contrast, an entB mutant of E. coli blocked in the conversion of isochorismate to 2,3-dihydro-2,3-dihydroxybenzoate formed salicylate when transformed with a pchB expression construct. Salicylate formation could also be demonstrated in vitro when chorismate was incubated with a crude extract of P. aeruginosa containing overproduced PchA and PchB proteins; salicylate and pyruvate were formed in equimolar amounts. Furthermore, salicylate-forming activity could be detected in extracts from a P. aeruginosa pyoverdin-negative mutant when grown under iron limitation, but not with iron excess. Our results are consistent with a pathway leading from chorismate to isochorismate and then to salicylate plus pyruvate, catalyzed consecutively by the iron-repressible PchA and PchB proteins in P. aeruginosa.
Mol Gen Genet 1995 Nov 15
PMID:Structural genes for salicylate biosynthesis from chorismate in Pseudomonas aeruginosa. 750 Sep 44

Random sequencing of cDNA and genomic libraries has been used to study the genome of the hyperthermophile Thermotoga maritima. To date, 175 unique clones have been analyzed by comparing short sequence tags with known proteins in the PIR and GenBank databases. We find that a significant proportion of sequences can be matched to previously identified protein from non-Thermotoga sources. A high match rate was obtained from an oligo(dT)-primed cDNA library, where one-third of all unique sequences analyzed (21/65) shared high amino acid sequence similarity with proteins in the PIR and GenBank databases. Also, approximately one-third of the unique sequences from a second cDNA library (28/89), constructed with random oligo primers, could be matched to sequences in PIR and GenBank. Identification of genes from the oligo(dT)-primed cDNA library indicates that some Thermotoga mRNAs are polyadenylated. Genes have also been identified from a 1 to 2 kb genomic DNA library. Here, (3/21) of genomic sequences analyzed could be matched to protein in PIR and GenBank. One of the genomic clones had high sequence similarity to the tryptophan synthesis gene anthranilate synthase component I (trpE). Using this sequence tag, the Thermotoga trp operon was isolated and sequenced. The Thermotoga maritima trp operon is arranged with trpE forming an overlapping transcript with a second protein consisting of a fusion of anthranilate synthase component II (trpG) and anthranilate phosphoribosyltransferse (trpD). With regard to the fusion, the operon organization is similar to Escherichia coli and Salmonella typhimurium, but lacks the classic attenuation system of enteric bacteria. Amino acid sequence comparison with 19 trpE, 18 trpG and 14 trpD genes from other organisms suggest that the Thermotoga trp genes resemble corresponding genes from other thermophiles more closely than expected.
J Mol Biol 1993 Jun 20
PMID:Studies of the hyperthermophile Thermotoga maritima by random sequencing of cDNA and genomic libraries. Identification and sequencing of the trpEG (D) operon. 768 30

The yeast TRP3 gene encodes a bifunctional protein with anthranilate synthase II and indoleglycerol-phosphate synthase activities. Replacing ten consecutive non-preferred codons in the indoleglycerol-phosphate synthase region of the TRP3 gene with synonymous preferred codons (to create the TRP3pr gene; translational pause replaced) causes a 1.5-fold reduction in relative indoleglycerol-phosphate synthase activity [Crombie, T., Swaffield, J.C. & Brown, A.J.P. (1992) J. Mol. Biol. 228, 7-12]. Here, we report that both the anthranilate synthase II and indoleglycerol-phosphate synthase domains are affected to similar extents when the translational pause is removed. Also, structural modelling of the yeast indoleglycerol-phosphate synthase domain against the X-ray crystal structure of indoleglycerol-phosphate synthase from Escherichia coli indicates that the translational pause lies in a region of structural divergence between similar structures. To probe the role of cytoplasmic heat-shock protein 70 (Hsp 70) chaperones in Trp3 protein folding, anthranilate synthase and indoleglycerol-phosphate synthase activities were measured in ssa and ssb mutants. Neither indoleglycerol-phosphate synthase nor anthranilate synthase were affected significantly in the ssb mutant. However, depletion of Hsp70 proteins encoded by the SSA genes led to decreased anthranilate synthase and indoleglycerol-phosphate synthase activities from the TRP3 gene, suggesting that both domains depend to some extent upon the SSA chaperone family. The data are consistent with roles for both the translational pause and Ssa chaperones in Trp3 protein folding in vivo.
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PMID:The folding of the bifunctional TRP3 protein in yeast is influenced by a translational pause which lies in a region of structural divergence with Escherichia coli indoleglycerol-phosphate synthase. 800 82

Plasmid clones capable of expressing a recombinant fusion proteins containing the anthranilate synthase of E. coli (TrpE) and different regions of gp46 HTLV-I were constructed on the basis of pATH-vectors. A high extent of TrpE-gp46 proteolytic degradation took place independently of the bacterial La-protease. Fusion proteins containing an N-terminal part of gp46 were more stable and could be purified in preparative quantities but were less antigenic. On the contrary, a TrpE-gp46 protein encoded by the TaqI-TaqI DNA fragment and containing only 35 C-terminal amino acids was still susceptible to degradation but possessed good serologic reactivity. Some of the recombinant proteins obtained can be useful for diagnostics and for preparing monoclonal or polyclonal antibodies.
Mol Biol (Mosk)
PMID:[Differential expression of recombinant hybrid proteins containing amino- and carboxy-terminal regions of the exterior large glycoprotein (gp46) of the human T-cell leukemia virus (HTLV-I) in Escherichia coli cells]. 848 63

The bacterial endosymbionts (Buchnera) from the aphids Rhopalosiphum padi, R. maidis, Schizaphis graminum, and Acyrthosiphon pisum contain the genes for anthranilate synthase (trpEG) on plasmids made up of one or more 3.6-kb units. Anthranilate synthase is the first as well as the rate-limiting enzyme in the tryptophan biosynthetic pathway. The amplification of trpEG on plasmids may result in an increase of enzyme protein and overproduction of this essential amino acid, which is required by the aphid host. The nucleotide sequence of trpEG from endosymbionts of different species of aphids is highly conserved, as is an approximately 500-bp upstream DNA segment which has the characteristics of an origin of replication. Phylogenetic analyses were performed using trpE and trpG from the endosymbionts of these four aphids as well as from the endosymbiont of Schlechtendalia chinensis, in which trpEG occurs on the chromosome. The resulting phylogeny was congruent with trees derived from sequences of two chromosome-located bacterial genes (part of trpB and 16S ribosomal DNA). In turn, trees obtained from plasmid-borne and bacterial chromosome-borne sequences were congruent with the tree resulting from phylogenetic analysis of three aphid mitochondrial regions (portions of the small and large ribosomal DNA subunits, as well as cytochrome oxidase II). Congruence of trees based on genes from host mitochondria and from bacteria adds to previous support for exclusively vertical transmission of the endosymbionts within aphid lineages. Congruence with trees based on plasmid-borne genes supports the origin of the plasmid-borne trpEG from the chromosomal genes of the same lineage and the absence of subsequent plasmid exchange among endosymbionts of different species of aphids.
J Mol Evol 1996 Apr
PMID:The tryptophan biosynthetic pathway of aphid endosymbionts (Buchnera): genetics and evolution of plasmid-associated anthranilate synthase (trpEG) within the aphididae. 864 10

Aphids obtain tryptophan from prokaryotic endosymbionts assigned to the genus Buchnera. The rate-limiting enzyme in tryptophan biosynthes, anthranilate synthase, is encoded by the genes trpE and trpG. In Buchnera within the family Aphididae, trpEG is plasmid-borne, apparently as an adaptation to overproduce tryptophan for hosts. To explore the evolution of these plasmids, sequences for trpEG, the upstream region containing the plasmid origin of replication, and chromosomal trpB were obtained for Buchnera of three species in the aphid genus Uroleucon and analyzed together with sequences for six other aphid species. Phylogenies based on trpB and trpEG agree with each other and with previous views of aphid phylogeny. Synonymous substitutions are about twice as high for plasmid-borne genes as for chromosomal genes in the same lineages, suggesting higher mutation rates for genes on plasmids. Nonsynonymous rates for trpEG are accelerated within Buchnera of Uroleucon, indicating a change in selection intensity within this genus. Accelerated evolution within Uroleucon also seems to characterize the upstream region containing the putative origin of replication.
Mol Phylogenet Evol 1997 Oct
PMID:Evolution of the tryptophan biosynthetic pathway in Buchnera (aphid endosymbionts): studies of plasmid-associated trpEG within the genus Uroleucon. 929 22

The biosynthetic pathway to 4-hydroxybenzoate (4HB), a precursor of the naphthoquinone pigment shikonin, was modified in Lithospermum erythrorhizon hairy root cultures by introduction of the bacterial gene ubiC. This gene of Escherichia coli encodes chorismate pyruvate-lyase (CPL), an enzyme that converts chorismate into 4HB and is not normally present in plants. The ubiC gene was fused to the sequence for a chloroplast transit peptide and placed under control of a constitutive plant promoter. This construct was introduced into L. erythrorhizon by Agrobacterium rhizogenes-mediated transformation. The resulting hairy root cultures showed high CPL activity. 4HB produced by the CPL reaction was utilized for shikonin biosynthesis, as shown by in vivo inhibition of the native pathway to 4HB with 2-aminoindan-2-phosphonic acid (AIP), an inhibitor of phenylalanine ammonia-lyase. A feeding experiment with [1,7-13C2]shikimate showed that in the absence of AIP the artificially introduced CPL reaction contributed ca. 20% of the overall 4HB biosynthesis in the transgenic cultures. ubiC transformation did not lead to a statistically significant increase of shikonin formation, but to a 5-fold increase of the accumulation of menisdaurin, a nitrile glucoside which is presumably related to aromatic amino acid metabolism.
Plant Mol Biol 1999 Mar
PMID:Genetic engineering of shikonin biosynthesis hairy root cultures of Lithospermum erythrorhizon transformed with the bacterial ubiC gene. 1035 83

The entire gene cluster encoding enzymes involved in biosynthesis of L-tryptophan in the hyperthermophilic archaeon Pyrococcus kodakaraensis KOD1 has been cloned and sequenced. Seven ORFs, which encode indole-3-glycerol phosphate synthase (trpC), anthranilate phosphoribosyltransferase (trpD), the two subunits of anthranilate synthase (trpEG), phosphoribosyl anthranilate isomerase (trpF) and the two subunits of tryptophan synthase (trpAB), were identified. The gene order is trpCDEGFBA, covering a region of 6045 bp. In order to confirm the function of the gene products, we expressed the first gene, Pk-trpC, in Escherichia coli. The protein product was purified, and was found to show the expected indole-3-glycerol phosphate synthase activity, with a temperature optimum of 85 degrees C. We could clearly identify a single mRNA transcript by Northern analysis using probes in the central and 3'-regions of the gene cluster, indicating that the gene cluster is transcribed as an operon. A significant increase in trp mRNA level was observed in cells grown in medium depleted of L-tryptophan, compared to cells grown in medium supplemented with L-tryptophan, indicating that expression of the gene cluster is regulated at the transcriptional level.
Mol Gen Genet 1999 Dec
PMID:The tryptophan biosynthesis gene cluster trpCDEGFBA from Pyrococcus kodakaraensis KOD1 is regulated at the transcriptional level and expressed as a single mRNA. 1062 65


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