Disease relevance of trpA

• Nucleotide sequences of trpA of Salmonella typhimurium and Escherichia coli: an evolutionary comparison [1].
• After our first observation of codon context effects in missense suppression ( Murgola & Pagel , 1983), we measured the suppression of missense mutations at two positions in trpA in Escherichia coli [2].
• Codon usage in these Pseudomonas genes shows a marked preference for codons ending in G or C, thereby resembling that of trpB, trpA, and several other chromosomal loci from this species and others with a high G + C content in their DNA [3].
• The suppressor allows readthrough of UGA mutations at two positions in trpA and at two sites in bacteriophage T4 [4].
• To reveal the properties and potential physiological role of TrpB2, the trpA, trpB1, and trpB2 genes of Thermotoga maritima were expressed heterologously in Escherichia coli, and the resulting proteins were purified and characterized [5].

High impact information on trpA

• In this study it is shown that, under conditions of intense selection, a strain carrying missense mutations in both trpA and trpB reverts to Trp+ 10(8) times more frequently than would be expected if the two mutations were the result of independent events [6].
• The suppressor also does not allow mistranslation of the UGA-related trpA missense mutations UGG at positions 211 and 234, AGA at 211 and 234, CGA at 211, or UGU and UGC at 234 [4].
• The TrpA and TrpB1 proteins are encoded by the adjacent trpA and trpB1 genes in the trp operon [5].
• The mutant alpha subunits, obtained by in vitro random, saturation mutagenesis of the encoding trpA gene, contain single amino acid substitutions at sites within the first 121 residues of the alpha polypeptide [7].
• Analysis of trpA expression in these deletion mutants established that the ribosome binding site sequence is required for efficient translation of the trpA segment of trp mRNA [8].

Chemical compound and disease context of trpA

• Downstream from trpA lies a Rho-independent terminator that resembles E. coli sequences that are situated downstream from the E. coli trp operon [9].
• We investigated whether there is translational coupling between the tryptophan operon trpB and trpA genes in Escherichia coli [10].
• We describe a novel class of missense suppressors that read the codons for lysine at two positions (211 and 234) in the trpA polypeptide of Escherichia coli [11].
• The Pseudomonas aeruginosa tryptophan synthase genes, trpA and trpB, which are induced by their substrate indoleglycerol phosphate, were cloned along with their controlling region into the BamHI site of pBR322 to produce the 10.7-megadalton plasmid pZAZ5 [12].
• Induction of specific base-pair substitutions in E. coli trpA mutants by chloroethylene oxide, a carcinogenic vinyl chloride metabolite [13].

Biological context of trpA

• Most of the nucleotide sequences can be assigned to specific locations in the structural genes, based on the amino-acid sequences of the trpB and trpA proteins [14].
• Missense and nonsense suppressor tRNAs, selected for their ability to read a new triplet codon, were observed to suppress one or more frameshift mutations in trpA of Escherichia coli [15].
• A modest effect of translation over the trpA ribosome binding site on independent initiation at that site was also observed [8].
• To examine the effect of stop codon location specifically, we constructed plasmids in which different nucleotide sequences preceding the trpA start codon were retained, and only the reading frame was changed [16].
• However, codon usage in K. aerogenes trpA reflects the high G+C content of the genome of this organism [17].

Anatomical context of trpA

• Certain Escherichia coli tryptophan synthase mutant alpha-subunits encoded from mutagenized trpA-containing plasmids were overexpressed as insoluble aggregates which were seen as large, intracellular inclusion bodies [18].

Associations of trpA with chemical compounds

• The mRNA sites of the codons correspond to amino acids 211 and 234 of the trpA polypeptide, positions at which glycine is the wild-type amino acid [2].
• The suppressible codons in the trpA messenger RNA were the lysine codons, AAA and AAG, and the glutamic acid codons, GAA and GAG [2].
• We also observed that excess N was able to suppress transcriptional polarity in the particular case of cloned 'trpA, the last gene of the tryptophan operon, although there was no effect on polarity within chromosomal trpE [19].
• The majority of the enzymatically defective mutant alpha subunits have decreased capacities for substrate (indole-3-glycerol phosphate) utilization, typical of the early trpA missense mutants isolated by in vivo selection methods [20].
• The mutagenized fragments were subcloned into the plasmid vector and used to transform to ampicillin resistance (Ampr) a recipient strain containing a UGA mutation in trpA [21].

Physical interactions of trpA

• To examine the dependence of trpA expression on the ribosome binding site sequence in the distal segment of trpB, deletions were produced that replaced this trpB sequence [8].

Other interactions of trpA

• Translation of trpB is terminated by single UGA codon, which overlaps the trpA AUG initiation codon: UGAUG [14].
• A trp-lac fusion system was used in which part of the trpA gene is fused to the lacZ gene [10].
• C-terminal deletions or fusions of the livK gene to trpA (encoding the alpha subunit of tryptophan synthetase) were secreted with little loss of efficiency [1] [22].

Analytical, diagnostic and therapeutic context of trpA

• A cDNA encoding Arabidopsis thaliana tryptophan synthase alpha(TSA1) was isolated by complementation of an Escherichia coli delta trpA mutation and by polymerase chain reaction amplification from a cDNA library using degenerate primers [23].
• These conclusions are drawn from experiments in which the two Ser codons UCU233 and UCG235 in a nonsense mutant form (UGA234) of the trpA gene in Escherichia coli have been replaced with other Ser codons by site-directed mutagenesis [24].

References