title: Expression of Shigella flexneri gluQ-rs gene is linked to dksA and controlled by a transcriptional terminator.
abstract: BACKGROUND
  Glutamyl queuosine-tRNA(Asp) synthetase (GluQ-RS) is a paralog of the catalytic domain of glutamyl-tRNA synthetase and catalyzes the formation of glutamyl-queuosine on the wobble position of tRNA(Asp). Here we analyze the transcription of its gene in Shigella flexneri, where it is found downstream of dksA, which encodes a transcriptional regulator involved in stress responses.
  
  
  RESULTS
  The genomic organization, dksA-gluQ-rs, is conserved in more than 40 bacterial species. RT-PCR assays show co-transcription of both genes without a significant change in transcript levels during growth of S. flexneri. However, mRNA levels of the intergenic region changed during growth, increasing at stationary phase, indicating an additional level of control over the expression of gluQ-rs gene. Transcriptional fusions with lacZ as a reporter gene only produced β-galactosidase activity when the constructs included the dksA promoter, indicating that gluQ-rs do not have a separate promoter. Using bioinformatics, we identified a putative transcriptional terminator between dksA and gluQ-rs. Deletion or alteration of the predicted terminator resulted in increased expression of the lacZ reporter compared with cells containing the wild type terminator sequence. Analysis of the phenotype of a gluQ-rs mutant suggested that it may play a role in some stress responses, since growth of the mutant was impaired in the presence of osmolytes.
  
  
  CONCLUSIONS
  The results presented here, show that the expression of gluQ-rs depends on the dksA promoter, and strongly suggest the presence and the functionality of a transcriptional terminator regulating its expression. Also, the results indicate a link between glutamyl-queuosine synthesis and stress response in Shigella flexneri.
authors.affiliation: Program of Microbiology and Mycology, Institute of Biomedical Science-ICBM, Faculty of Medicine, University of Chile, Santiago, Chile.
authors.forename: Valeria C
authors.initials: VC
authors.lastname: Caballero
authors.forename: Viviana P
authors.initials: VP
authors.lastname: Toledo
authors.forename: Cristian
authors.initials: C
authors.lastname: Maturana
authors.forename: Carolyn R
authors.initials: CR
authors.lastname: Fisher
authors.forename: Shelley M
authors.initials: SM
authors.lastname: Payne
authors.forename: Juan Carlos
authors.initials: JC
authors.lastname: Salazar
mesh_terms: D000604:Amino Acyl-tRNA Synthetases / Q000235:genetics / Q000378:metabolism*; D019677:Artificial Gene Fusion; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D019295:Computational Biology; D004252:DNA Mutational Analysis; D015964:Gene Expression Regulation, Bacterial; D023061:Gene Order; D017930:Genes, Reporter; D011401:Promoter Regions, Genetic; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017384:Sequence Deletion; D012763:Shigella flexneri / Q000235:genetics* / Q000378:metabolism*; D026801:Synteny; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D061806:Transcription Termination, Genetic; D001616:beta-Galactosidase / Q000032:analysis / Q000235:genetics
chemical_list: D001426:Bacterial Proteins; D014157:Transcription Factors; D001616:beta-Galactosidase; D000604:Amino Acyl-tRNA Synthetases