Disease relevance of truA

• A 9.7-kilobase pair segment of the Escherichia coli chromosome spanning the hisT and purF loci has been characterized [1].
• The truA gene of Pseudomonas aeruginosa is required for the expression of type III secretory genes [2].
• We show here that strain EB146 (leuK16) has properties that are similar to those of E. coli and Salmonella typhimurium hisT strains [3].
• Insertion of mini-Mu d1 (lac Km) phage into plasmid psi 300 confirmed that the hisT gene is the downstream gene in the operon [4].

High impact information on truA

• Evidence is presented that hisT mutants (which lack pseudouridine in the anticodon arm of histidine tRNA) may cause derepression of the his operon by slowing protein synthesis in the leader peptide gene [5].
• In the absence of other proteins, purified tRNA pseudouridine synthase I forms psi at all three modification sites known to be affected in hisT mutants [6].
• Two other genes, denoted dedC and dedD, have been localized between the hisT and purF operons [1].
• The distal hisT gene encodes the tRNA modification enzyme, pseudouridine synthase I, which was shown to have a polypeptide molecular mass of 30,399 daltons [7].
• The DNA sequence was consistent with the phenotypes and hisT expression of mutant operons [7].

Chemical compound and disease context of truA

• 1H-15N NMR studies of Escherichia coli tRNA(Phe) from hisT mutants: a structural role for pseudouridine [8].
• Escherichia coli tRNA(Phe)U39 was isolated from a specially constructed bacterial strain (DD1003/pRK3) carrying mutations in the hisT gene (the structural gene for tRNA pseudouridine synthase I) and in the pyrB gene (uracil auxotrophy) [8].
• Four phenotypes of strain EB146 (leuK16), leucine excretion, wrinkled colony morphology, and elevated levels of leu and his enzymes, are complemented by a plasmid having a 1.65-kilobase DNA fragment containing the E. coli K-12 hisT locus [3].
• Structural analysis of the Escherichia coli K-12 hisT operon by using a kanamycin resistance cassette [9].
• A locus (leuK) affecting regulation of the leucine operon was selected by isolating a spontaneous Ara+ derivative of an Escherichia coli B/r strain carrying an ara-leu fusion in which the arabinose operon is under leucine control [10].

Biological context of truA

• Indeed, a truA mutant is defective in type III gene expression while its twitching motility is unaffected, and a truA clone is able to complement the type III secretion defect [2].
• Pseudouridination of tRNAs is important for tRNA structure, thereby improving the fidelity of protein synthesis and helping to maintain the proper reading frame; thus the results imply that truA controls tRNAs that are critical for the translation of type III genes or their regulators [2].
• The DNA sequence of a 2,3-kilobase segment of the E. coli hisT operon was determined [7].
• There is very little protein sequence homology between the truB gene product and the hisT (truA) product, which forms psi in the anticodon arm of tRNAs [11].
• Subclones containing restriction fragments from plasmid psi 300 inserted downstream from the lac promoter established that the hisT gene is oriented from the HindIII site toward the ClaI site [4].

Associations of truA with chemical compounds

• Expression in both of these mutants was unaltered by the presence of the hisT allele or by the addition of threonine and isoleucine to the growth medium [12].
• In a hisT strain (which has altered leucyl-tRNA), transhydrogeanse was at a repressed level without the addition of leucine, suggesting that leucyl-tRNA may be involved in the regulation [13].
• Furthermore, in tRNA3Leu and tRNA4Leu from a leuK strain, uridine residues at positions 39 and 40, respectively, are unmodified [3].
• A new locus (leuK) affecting the regulation of branched-chain amino acid, histidine, and tryptophan biosynthetic enzymes [10].
• However, the level of derepression of DAP-decarboxylase, the last enzyme of the lysine pathway, is very low in the hisT mutant; this indicates that tRNAlys is a secondary effector involved in the regulation of the synthesis of this enzyme [14].

Physical interactions of truA

• Thus, pdxB must be the first gene in the complex pdxB-hisT operon [15].

Other interactions of truA

• We show that the minimum size of the operon is approximately 3,500 base pairs and that it contains at least four genes, which are arranged in the order usg-2 (pdxB), usg-1, hisT, and dsg-1 and encode polypeptides with apparent molecular masses of 42,000, 45,000, 31,000, and 17,000 daltons, respectively [9].
• An example using this technique in which the product of the usg gene in the hisT operon of E. coli has been purified and biochemically characterized is described [16].

Analytical, diagnostic and therapeutic context of truA

• Sequence analysis showed that the insertion disrupted hisT, the gene encoding pseudouridine synthase I, a tRNA-modifying enzyme. hisT::Tn5 mutant cells were also shown to be defective for the production of other antibiotic peptides, such as microcin C7, microcin H47, and colicin V [17].
• Transductional analysis showed that the altered regulation is due to the presence of a mutation in hisT, the gene for the tRNA modification enzyme pseudouridine synthetase I. A complementation test showed that the regulatory defect conferred by the hisT mutation was recessive [18].

References